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SDec'SB 


HEREDITY   AND    EUGENICS 


HEREDITY    AND 
EUGENICS 


BY 

R.    RUGGLES    GATES,    Ph.D.,    F.L.S. 

PROFESSOR    OF    EOTAKY    IN    1  HE    UNIVERSITY    OK    LONDO.N    A.ND    HEAD   OF    THE 

DEPARTMENT    OF    BOTANY    AT    KING'S    COLLEGE: 

SOMETI.ME    ASSOCIATE    PROFESSOR   OF    ZOOLOGY,     UNIVERSITY    OF    CALIFoKNIA; 

AUTHOR   OF    "the    MUTATION    FACTOR    IN    EVOLUTION,"    ETC. 


CONSTABLE    AND    CO.    LTD, 

LONDON  BOMBAY         SYDNEY 

1923 

fltO^ERTT  mRARY 

N.  C.  SiMte  C^Uegf 


PRINTED    IN    GREAT    BRITAIN    BY 
BILLING    AND    SONS,    LTD.,    GUILDFORD    AND    ESHER 


TO 

MY    MOTHER 

THIS    BOOK   IS   AFFECTIONATELY   DEDICATED 


QlH-i 


„■    .r.,; 


PREFACE 

This  book  has  been  written  partly  by  the  accident  of 
circumstances  and  partly  by  request.  It  is  based 
upon  a  couple  of  articles  which  appeared  in  the 
Eugenics  Review  for  January  and  April,  1920,  and 
part  of  it  was  written  during  a  holiday  in  America  in 
1 92 1.  Although  m}'  present  interests  are  occupied 
with  the  field  of  modern  botany,  I  was  impelled  to 
write  this  book  by  my  interest  in  Eugenics,  which  is 
in  turn  founded  upon  a  knowledge  of  genetics.  The 
actual  writing  of  it  was,  however,  only  made  possible 
by  the  many  friends  in  various  parts  of  the  world  who 
have  sent  me  their  publications. 

It  is  clear  to  scientific  men,  although  rarely  to 
statesmen  and  law-makers,  that  any  intelligent 
attempt  to  improve  the  conditions  and  qualities  of  the 
human  race  must  be  founded  upon  some  knowledge 
of  the  manner  in  which  these  qualities  arise  and  are 
inherited  and  maintained  or  lost.  In  this  book  I  have 
confined  myself  as  strictly  as  possible  to  an  examina- 
tion of  the  facts  of  human  inheritance,  in  so  far  as 
they  are  at  present  known,  and  I  have  laid  particular 
emphasis — possibly  too  much — upon  the  many  cases 
now  known  of  Mendelian  inheritance  in  man.  This 
is  not  on  account  of  any  partiality  for  this  particular 
form  of  inheritance;  but  because  the  Mendehan 
differences  are  clear  cut  and  more  easily  recognised, 
and  the  manner  of  their  inheritance  is  more  easil}^ 
traced  and  analysed  and  investigated  than  that  of 
differences  which  can  only  be  recognised  as  quantita- 

vii 


viii  PREFACE 

tive,  and  whose  precise  manner  of  inheritance  must 
still  be  regarded  as  under  discussion. 

The  literature  of  the  last  two  decades  has  recorded 
many  cases  of  Mendelian  inheritance  in  man,  as  the 
present  book  will,  I  think,  testify.  But  it  will  also 
be  seen  that  even  the  pre-Mendelian  literature 
contained  many  scattered  records  of  great  interest 
which  are  now  seen  to  fall  into  the  Mendelian  categories 
of  explanation.  I  have  made  no  attempt  to  search 
the  literature  exhaustively,  as  the  work  is  really  only 
a  by-product  of  my  own  evolutionary  interests, 
but  I  hope  that  no  records  of  first-rate  importance 
have  been  omitted,  and  I  believe  that  several  valuable 
early  papers  are  here  for  the  first  time  brought  into 
orientation  with  the  twentieth-century  literature. 
The  book  might  easily  have  grown  to  considerably 
greater  proportions,  but  I  have  endeavoured  to  include 
only  the  more  essential  subjects  and  discussions  which 
a  book  of  this  kind,  written  from  the  biological  point  of 
view,  ought  to  contain.  Whenever  experiments  with 
animals  or  plants  bear  directly  on  the  topic  in  hand, 
I  have  not  hesitated  to  use  them,  and  I  trust  this 
will  add  to  the  value  of  the  w^ork,  both  to  the  general 
public  interested  in  Eugenics,  and  the  medical 
profession,  who  should  always  be  on  the  alert  to 
detect  the  inheritance  element  which  so  frequently 
is  present  in  the  functional  derangements  with  which 
they  have  to  deal. 

Many  matters  which  are  primarily  of  genetic 
interest,  but  without  at  present  any  special  bearing 
on  human  heredity,  have  been  omitted  altogether. 
If  this  work  aids  in  the  diffusion  of  an  intelligent 
interest  and  understanding  of  heredity  in  its  bearing 
on  the  welfare  of  future  generations,  its  object  will 
have  been  achieved.  The  conceptions  of  heredity 
are  no  longer  vague  and  ill-defined,  as  in  the  writings 
of  a   generation   ago.     They   are   clear   and   sharply 


PREFACE  ix 

defined,  and  are  based  on  much  accurate  knowledge 
of  organic  structure  and  development.  The  germ 
plasm  of  the  race  is  a  uniquely  precious  material, 
and  its  conservation  and  improvement  in  each  genera- 
tion should  be  the  first  aim  of  the  State.  The  first 
essential  for  such  a  conservation  is  the  recognition  of 
the  inherent  (inherited)  differences  in  the  capacities 
of  individuals.  Everything  goes  to  show  that  once 
a  particular  strain  of  germ  plasm  is  lost,  it  is  gone  for 
ever.  In  State  recognition  of  the  value  of  human 
germinal  qualities,  perhaps  no  country  has  equalled 
Sweden,  where  family  records  and  genealogies  have 
been  kept  for  centuries  in  an  exceptionally  complete 
form,  and  where  race  biology  is  already  recognised  as 
a  subject  of  the  greatest  national  importance. 

While  it  is  necessary  to  recognise  the  fundamental 
importance  of  inherited  physical  and  mental  differ- 
ences, as  the  foundation  of  Eugenics,  one  must 
also  remember  that  environment  counts  in  the  sense 
that  a  favourable  or  suitable  environment  is  required 
to  bring  out  the  potential  qualities  of  any  develop- 
ing organism.  Nevertheless,  it  is  these  potential 
(germinal)  differences  on  which  the  Eugenist  must 
rely  in  any  effort  to  improve  the  race  or  direct  the 
selection  of  germinal  qualities  which  is  going  on  in 
every  generation. 

In  conclusion,  I  wish  to  thank  those  who,  in  various 
ways,  have  contributed  to  the  production  of  this 
book.  I  am  indebted  to  Professor  R.  C.  Punnett, 
F.R.S.,  for  permission  to  publish  Figs.  4,  ii,  and  12, 
from  the  Journal  of  Genetics  ;  to  Sir  Arthur  Keith, 
F.R.S.,  for  the  loan  of  the  blocks  from  the  Journal  of 
Anatomy  and  Physiology,  January,  191 6,  which 
illustrate  Figs.  13  and  14;  to  the  Royal  Society  of 
Medicine  for  permission  to  reproduce  Fig.  15  (from 
Proc.  Roy.  Soc.  Med.  {Path.),  vol.  x.,  p.  60);  and  to 
the  editorial  board  of  the  Journal  of  Heredity,   for 


X  PREFACE 

permission  to  republish  the  photographs  of  twins 
in  Figs.  29  to  34.  Professor  J.  A.  Piatt  has  kindly 
supplied  the  original  reference  to  Caesar's  horse,  and 
I  am  indebted  to  Professor  F.  J.  C.  Hearnshaw  for 
certain  historical  references.  I  am  very  much  in- 
debted to  Professor  E.  W.  MacBride,  F.R.S.,  for 
kindly  reading  the  proof-sheets  and  offering  many 
valuable  suggestions  and  criticisms;  also  to  Professor 
A.  Dendy,  F.R.S.,  for  certain  suggestions.  I  alone, 
however,  am  responsible  for  the  views  expressed. 


R.  RUGGLES  GATES. 


King's  College, 

University  of  London, 

December  27,   1922. 


CONTENTS 


CHAPTER  PAGE 

I.    INTRODUCTION         -  -  -  -  -  -  I 


DEFINITION    OF   HEREDITY. 

II.    THE    GENERAL   ASPECTS    OF   HEREDITY     -  -  -  8 

INHERITANCE  OF  DIFFERENCES — MENDELISM — INHERIT- 
ANCE   OF    RESEMBLANCES DEVELOPMENT. 

III.  INHERITANCE   OF  PHYSICAL   CHARACTERS   IN   MAN  -  27 

y  STATURE EYE      COLOLfR SKIN      COLOUR     AND      HAIR 

CHARACTERS ALBINISM LEFT-HANDEDNESS 

DIGITAL    ABNORMALITIES VARIOUS     ABNORMALI- 
TIES. 

IV.  INHERITANCE    OF    MENTAL    CHARACTERS    IN    MAN  -  -       I45 

FEEBLE-MINDEDNESS INSANITY CACOGENIC       FAMI- 

LIES MUSICAL    ABILITY HANDWRITING. 

V.    THE    LIMITS    OF   HEREDITY  -  -  -  -       1 75 

TWINS FINGER   PRINTS INHERITANCE    OF   TWINNING 

LETHAL    FACTORS. 

VI.    SOCIAL    AND   WORLD    ASPECTS    OF   EUGENICS  -  -       204 
THE   BASIS    OF   RACIAL   AND    TEMPERAMENTAL   DIFFER- 
ENCES  THE     RESULTS     OF     CROSSING     BETWEEN 

RACES THE  PROBLEMS  OF  POPULATION POPULA- 
TION AND  QUALITY. 

LIST  OF  GENERAL  WORKS   BEARING  ON  EUGENICS         -  -      252 

BIBLIOGRAPHY   OF   PAPERS   CITED   IN   THE   TEXT  -  -254 

INDEX  -  -  -  -  -  -  -       273 


LIST   OF    ILLUSTRATIONS 

FIC"  I'AGE 

1.  DIAGRAM    OF    NORMAL  X  BRA CHYDACTYL  -                  -  -  lO 

2.  DIAGRAM    OF    BRACHYDACTYL  X  BRACK YDACTYL   -  -  II 

3.  DIAGRAM    OF    HETEROZYGOTE  X  HOMOZYGOTE          -  -  12 

4.  ANTHER    SHOWING    SEGREGATION                    -                   -  -  I5 

5.  DIAGRAM    OF    DOMINANT  X  RECESSIVE,    F^                   -  -  18 

6.  DIAGRAM    SHOWING    THE    Fo    IN    THE    ABOVE    CROSS  -  18 

7.  DIAGRAM    OF    SEX    CHROMOSOMES                    -                   -  -  I9 

8.  DIAGRAM  OF  INHERITANCE  OF  SEX-LINKED  CHARACTERS-  23 

9.  PEDIGREE   OF   TORTOISESHELL-COLOURED    EYES    -  -  49 

10.  PEDIGREE   OF  BOLLENBACH  FAMILY              -                   -  "  5^ 

11.  PEDIGREE    OF    WHITE    FORELOCK                    -                   -  -  62 

12.  PEDIGREE    OF   ALBINIS:\I                       -                   -                   -  -  67 

13.  BRACHYDACTYLOUS  AND   NORMAL  HANDS                    -  -  79 

14.  RADIOGRAM  OF  A  BRACHYDACTYLOUS  HAND             -  -  80 

15.  ABNORMAL  SEGMENTATION  OF  FINGERS     -                   -  -  84 

16.  RADIOGRAPH  OF  HANDS  OF  A  GIRL  IN    THE   SAME  FAMILY  85 

17.  SKIAGRAM  OF  HANDS   OF  A.T.           -                   -                   -  -  87 

18.  PEDIGREE    OF    HEXADACTYLY         -                   -                   -  -  IO4 

19.  PEDIGREE    OF    HEXADACTYLOUS    FAMILY                    -  -  IO5 

20.  PEDIGREE    OF    COLOUR-BLINDNESS                 -                   -  -  112 

21.  PEDIGREE    OF   FEMALE   SEX-LINKED    BLINDNESS  -  -  II 7 

22.  PEDIGREE    OF    MALE    SEX-LINKED    BLINDNESS        -  -  II7 

23.  PEDIGREE  OF  MALE    SEX-LINKED  ICHTHYOSIS         -  -  I18 

24.  PEDIGREE  OF  FEMALE    SEX-LINKED    COLOUR-BLINDNESS-  I18 

25.  PEDIGREE    OF    CLEFT    IRIS                  -                   -                   -  -  I20 

26.  PEDIGREE    OF    EARLY    DECAY    OF    TEETH                     -  -  1 24 

27.  PEDIGREE    OF    RIGHT    BILOBED    Ex\R             _                   -  -  13^ 

28.  PEDIGREE    OF    SMALL    PIT    IN    LEFT    EAR-                   -  -  I36 

29.  PEDIGREE    OF    IMBECILITY    IN    FEMALE    LINE           -  -  1 54 

30.  IRISH    SAILOR    TWINS           -                   -                   -                   -  -  1 82 

31.  THEIR    FINGER    PRINTS      -                   -                   -                  -  -  1 83 

32.  TWINS    FROM    YORK,    PENN.               -                   -                   -  -  1 84 

33.  TWINS,    MEN            -__--_  185 

34.  TWINS,    WOMEN,    MICHIGAN               -                   _                  -  -  186 

35.  TWIN    SISTERS,    SWITZERLAND        -                  -                  -  -  1 86 


XUl 


HEREDITY   AND    EUGENICS 

CHAPTER  I 

INTRODUCTION 

The  central  problem  of  evolution  is  still  the  nature 

and  causes  of  variation,  while  the  practical  problems 

of  eugenics  centre  about  heredity.     Variation  in  past 

ages  has  already  endowed  the  human  race  with  an 

almost    infinite    variety    of    types    and    characters, 

many  of  the  latter  alternative  in  their  inheritance. 

We  have  only  to  compare  those  we  know  best  with 

their  relatives  and  ancestors  to  realise  how  minute 

are  the  resemblances  and  differences  which  ma}^  be 

handed  on  to  descendants  and  collateral  lines.     These 

are,  no  doubt,  chiefly  a  matter  of  biological  inheritance, 

though  similarity  of  environment  may  play  a  part 

in  certain   cases.     Probably   in   no   other   species   of 

animal  or  plant  does  the  number  of  differences  between 

individuals  approach  the  number  to  be  observed  in 

man.     This  is  to  be  expected,  because  of  the  mental 

and  physical  complexity  of  the  human  organism;  but 

it  does  not  imply  greater  intrinsic  variability  than  in 

other  animals  or  plants. 

Given  this  enormous   complexity  of  types  in  the 

human  species,  and  the  inheritance  of  the  innumerable 

differences  involved,  it  follows  that  the  matings  of 

the  present  generation  determine  the  characteristics 

which  will  be  handed  on  to  future  generations.     A 

knowledge  of  inheritance  must,  therefore,  form  the 

basis   of  any   enlightened   attempt   to   influence   the 

I  I 


2  HEREDITY  AND  EUGENICS 

future  development  of  the  human  race,  which  Sir 
Francis  Galton  originally  contemplated  in  the  Eugenic 
Movement.  Popular  writers  frequently  venture  to 
deny  the  importance  of  heredity  to  mankind.  They 
are  willing  to  concede  its  cogency  in  animals,  and, 
in  fact,  practical  breeders  of  horses  and  dogs  and  other 
domestic  animals  rely  upon  heredity  to  perpetuate 
even  slight  differences  in  their  strains.  But  they  are 
often  unwilling  to  accept  for  mankind  the  principles 
of  heredit}'  which  they  themselves  have  practised 
or  seen  in  operation  in  other  animals.  Even  those 
w^ho  recognise  that  the  principles  of  heredity  must  be 
the  same  for  mankind  as  regards  physical  characters, 
are  sometimes  inclined  to  deny  that  the  same  laws 
hold  for  mental  characteristics. 

It  is  therefore  hoped  that  this  book  ma}^  help  to 
bring  the  reader  to  a  truer  perspective  regarding  the 
nature  and  meaning  of  heredity,  and  its  fundamental 
bearing  on  the  future  of  the  human  race.  False 
conceptions  regarding  inheritance  are  widespread, 
and  this  is  not  surprising  in  view  of  the  complexity 
of  the  subject  and  the  general  lack  of  education  in 
the  biological  sciences.  Only  in  the  last  tw^o  decades, 
through  experimental  investigations  with  plants  and 
animals,  has  any  clear  road  been  found  through  a 
mass  of  complicated  data.  It  may  now  be  claimed, 
however,  that  the  general  mechanism  of  heredity 
is  well  understood  in  many  cases,  and  although,  as 
in  every  science,  complications  continually  arise  with 
further  knowledge,  the  principles  already  understood 
will  form  a  sound  basis  for  future  advance. 

It  is  impossi-ble  in  this  book  to  consider  the  whole 
field  of  heredity  in  general  terms.  For  that  purpose, 
reference  ma}^  be  made  to  various  works  on  the  subject 
which  have  appeared  in  recent  years,  during  which  the 
field  of  genetics  has  been  an  extremely  active  one. 
In  this  w^ork  an  effort  will  be  made  to  bring  together 


INTRODUCTION  3 

the  more  important  data  on  human  heredity  which 
have  accumulated  chiefly  in  the  last  twenty  years ; 
but  the  general  principles  will  be  briefly  discussed, 
and  reference  will  be  made  to  experiments,  particu- 
larly with  regard  to  the  higher  animals,  when  the 
results  bear  directly  upon  problems  of  human  heredity. 
It  w^ill  be  seen  that  a  large  amount  of  information  has 
already  been  gained  regarding  the  inheritance  of  a 
multitude  of  traits,  both  physical  and  mental,  in 
mankind.  And  perhaps  the  most  surprising  feature 
of  these  results  is  the  minuteness  and  variety  of  the 
differences  which  are  now  known  to  follow  definite 
laws  of  inheritance.  But  it  is  not  necessary  to  rely 
upon  recent  work  to  establish  the  minuteness  and 
peculiarity  of  some  of  the  differences  which  are 
inherited  in  man.  Darwin,  who  was  unsurpassed 
as  an  observer,  and,  what  is  equally  important,  a 
collator  of  the  observations  of  others,  has  a  chapter 
on  blushing  in  his  book,  The  Expression  of  the  Emo- 
tions, in  which  (p.  312)  he  cites,  not  only  a  number 
of  cases  of  the  inheritance  of  a  tendency  to  blush, 
but  also  one  in  which  mother  and  daughter  blushed 
in  the  same  peculiar  manner.  The  tendency  to  blush 
excessively  is  due  to  a  psychological  peculiarity, 
while  the  distribution  of  the  area  over  which  a  blush 
spreads  must  have  a  physical  basis.  That  gait, 
gestures,  voice,  and  general  bearing  are  inherited, 
was  recognised  in  the  scientific  writings  of  over  a 
century  ago,  though  imitation  may  also,  of  course, 
play  a  part  here,  but  this  is  excluded  in  some  cases. 

Further  random  examples  of  inheritance  in  man 
will  not  be  cited  here,  but  the  reader  is  invited  to 
consider  the  mass  of  evidence  found  in  the  body  of 
this  book.  It  is  believed  that,  in  this  way,  any  reader 
who  is  inclined  to  doubt  the  universality  and  import- 
ance of  heredity  in  mankind  will  attain  a  truer  per- 
spective  regarding   the   whole   matter.     But   certain 


4  HEREDITY  AND  EUGENICS 

misconceptions  need  to  be  pointed  out  first.  The 
question  is  often  asked  whether  heredity  or  environ- 
ment is  more  important  in  connection  with  develop- 
ment. But  the  question  cannot  rightly  be  asked 
in  this  way,  because  any  organism  is  the  result  of 
continuous  complicated  reactions  and  interactions, 
not  onl}^  between  the  developing  germ  and  its  environ- 
ment, but  also  between  the  different  parts  of  the 
organism  itself.  Moreover,  it  is  quite  incorrect  to 
assume  that  the  organic  germ  and  the  environment 
mutually  react  with  each  other  in  any  simple  way. 
A  particular  change  in  the  environment  ma}^  con- 
spicuously affect  one  part  of  the  developing  organism 
without  visibly  affecting  other  parts.  Thus  Stockard 
(1909)  showed  that  when  magnesium  chloride  is 
added  to  the  sea  water  in  which  certain  fish  embryos 
are  developing,  c3xlopean  fishes  are  produced,  with 
one  median  eye  instead  of  two  lateral  ones.  This  is 
a  surprising  reaction  of  the  organism,  and  more 
particularly  of  the  nervous  system,  to  a  definite 
environmental  stimulus.*  Some  differences  in  the 
environment  will  therefore  produce  very  marked 
effects  on  the  developing  organism. 

On  the  other  hand,  organisms  developing  in  the 
same  environment  may  show  marked  differences, 
because  they  have  inherited  different  characters. 
Tw^o  hen's  eggs  in  an  incubator,  under  the  same  con- 
ditions of  temperature,  moisture,  etc.,  may  develop 
birds,  one  with  a  rose  comb  and  the  other  with  a 
single  comb,  or  one  with  white  feathers  and  the  other 
with  brow^n.  Obvioush^  the  environment  is  not  a 
differential,  but  the  difference  was  in  the  original 
eggs  and  is  inherited  from  the  previous  generation. 

*  Stockard 's  result  has  recently  been  shown  to  be  due  to 
differential  destruction  of  the  nerve  plate  in  the  embryo,  the 
destruction  beginning  at  the  anterior  end,  as  in  Child's  experi- 
ments with  potassium  cyanide. 


INTRODUCTION  5 

No  one  would  suggest  that  even  if  the  eggs  were 
incubated  at  different  temperatures  the  single  comb 
would  be  altered  to  a  rose  comb. 

Clearl}',  then,  some  characters  are  produced  by  an 
environmental  stimulus  and  others  are  determined 
by  inheritance,  although  in  both  cases  interaction 
of  organism  and  environment  takes  place  in  the 
development  of  the  character.  A  given  character 
may  occur  in  either  or  both  categories.  Thus  fascia- 
tion  or  flattening  of  the  stem  in  plants  usually  results 
from  over-nutrition  and  is  then,  as  a  rule  at  least, 
not  inherited  at  all.  But  in  Celosia  cristata,  the 
coxcomb  of  gardens,  extreme  fasciation  is  a  specific 
character,  distinguishing  this  form  from  C.  pluniosa. 
Again,  thickening  of  the  epidermis  or  formation  of 
corns  results  from  friction  of  the  skin  of  the  hands  or 
feet,  and  is  not  inherited.  But  keratosis  is  an  inherited 
condition  in  which  there  is  abnormal  thickening  of 
the  skin  without  any  excessive  friction. 

When  a  new  character  appears  through  a  variation, 
the  first  question  one  asks  is  whether  it  is  inherited. 
It  is  impossible  to  determine  this  with  certainty 
except  by  experiment — i.e.,  by  breeding  from  the  new 
type.  If  it  is  inherited,  one  must  conclude  that  a 
germinal  change  has  taken  place,  leading  to  the 
production  of  a  new  character,  or  at  least  that  a 
germinal  rearrangement  has  taken  place,  making 
possible  the  appearance  of  the  new^  character.  If 
it  is  not  inherited,  then  the  conclusion  is  that  a 
modification  has  been  impressed  on  the  organism 
by  some  feature  of  the  environment.*  The  question 
to  ask,  then,  is  not  whether  heredity  or  environment 

*  The  possibility  of  the  inheritance  of  acquired  characters  has 
not  been  considered  here,  because  if  it  ever  occurs  in  mankind 
it  is  probably  too  slow  in  its  action  to  affect  the  practical  problems 
of  eugenics.  The  subject  has  been  discussed  from  an  evolu- 
tionary point  of  view  elsewhere  (Gates,  192 1,  chap,  viii.-xii.). 


6  HEREDITY  AND  EUGENICS 

is  more  important  in  the  ontogeny  of  any  character, 
but  whether  a  difference  (variation)  which  appears 
in  an  organism  is  due  primarily  to  a  difference  in  the 
environment  or  a  difference  in  heredity  {cf.  Sumner, 
1922). 

This  leads  us  to  emphasise  a  point  w^hich  is  not 
always  recognised — namely,  that  the  relation  between 
the  organism  and  its  environment  is  not  the  simple 
and  direct  relation  between  two  reacting  chemical 
substances — it  is  rather  one  of  stimulus  and  re- 
sponse. It  is,  moreover,  clear  that  not  all  elements 
of  the  environment  are  equally  effective  in  modifying 
the  organism.  For  example,  a  change  in  the  light 
may  have  a  striking  effect  on  the  development  of 
one  organism  and  no  appreciable  effect  on  another. 
The  relations  of  an  organism  to  its  environment  are 
therefore  extremely  complex,  and  can  only  be  under- 
stood after  elaborate  analysis.  But  the  higher 
organisms,  and  particularly  man,  have  many  regula- 
tory mechanisms  which  enable  him  to  triumph  over 
extreme  variations  in  the  environment  without  being 
vitally  affected  b}^  them.  This,  with  his  weapons 
and  his  intelligence,  has  enabled  mankind  to  people 
the  four  corners  of  the  earth  in  almost  everv  extreme 
of  climatic  conditions  w^here  organisms  can  live  at  all. 
From  a  eugenic  point  of  view  it  is  to  be  remembered 
that  while  hereditary  differences  of  all  kinds  are  per- 
petuated in  all  conditions,  yet  optimum  conditions 
are  desirable  for  the  full  expression  of  the  characters 
inherited  by  the  organism.  From  this  it  follows 
that  those  who  insist  upon  the  importance  of  heredity 
in  perpetuating  good  stocks  should,  at  the  same  time, 
realise  the  desirability^  of  creating  an  environment 
in  which  the  best  ph3^sical,  mental,  and  moral  qualities 
of  the  individuals  can  find  free  expression. 

Before  proceeding  further  it  may  be  well  to  point 
out  that  whereas  heredity   w^as  formerly   defined  or 


INTRODUCTION  7 

measured  by  the  degree  of  resemblance  between 
parents  and  offspring,  this  treatment  of  the  subject 
will  no  longer  suffice.  Thus  Brooks  (1906)  says, 
C"  So  far  as  the  word  is  used  inductively  in  biology, 
heredity  is  the  resemblance  of  child  to  parent,  of 
offspring  to  ancestor,  while  the  difference  between 
parent  and  child  is  called  variation."  The  study 
of  alternative  inheritance,  which  appears  to  be  the 
most  usual  form  of  heredity,  has  made  it  necessary 
to  revise  such  a  definition  of  heredity,  as  well  as  our 
outlook  with  regard  to  its  incidence.  It  has  now 
become  a  commonplace  of  observation  that  the 
differences  between  organisms,  as  well  as  their 
resemblances,  are  often  inherited,  i  If  a  tall  is  crossed 
with  a  dwarf  variety,  we  know  that  usually  the  second 
generation  will  inherit  tallness  and  dwarfness — 
the  parental  differentiating  characters — in  a  definite 
proportion,  and  that  certain  of  the  tall  individuals 
will  go  on  transmitting  dwarfness.  We  may  even 
cross  two  white  varieties  of  plants  or  two  albino 
animals,  externally  alike,  and  obtain  coloured  off- 
spring. Yet  we  know  that  the  colour  in  this  case  is 
not  the  result  of  variation.  One  of  the  necessary 
elements  in  its  production  has  been  inherited  from 
each  parent,  though  neither  possesses  both.  In 
such  instances  invisible  (probably  nuclear)  differences 
have  been  inherited  which,  when  combined,  produce 
a  striking  externalised  difference.  Hence  it  is  neces- 
sary, in  speaking  of  inheritance,  to  recognise  that 
both  similarities  and  differences  may  be  inherited, 
the  one  quite  as  truly  as  the  other.  Some  of  the 
differences,  particularly  the  quantitative  ones,  which 
appear  in  offspring  may,  then,  be  the  result  of  varia- 
tion, germinal  or  otherwise;  but  many  of  them  will 
be  the  result  of  inheritance. 


CHAPTER  II 

THE  GENERAL  ASPECTS  OF  HEREDITY 

Many  vague  conceptions  of  heredity  were  formerly 
held,  and  much  ink  was  unprofitably  spilled  in  an  effort 
to  explain  or  elucidate  inheritance  in  the  absence 
of  adequate  experiment.  Human  inheritance  par- 
ticularly has  been  the  subject  of  innumerable  crude, 
unscientific  conceptions  such  as  "  failure  "  of 
inheritance  when  a  particular  trait  does  not  appear 
in  every  generation,  a  belief  in  maternal  impressions, 
or  scepticism  regarding  the  inheritance  of  mental 
traits.  The  scientific  investigation  of  heredity  may 
almost  be  said  to  have  begun  with  Mendel's  studies 
of  single  characters  in  garden  peas,  since  the  results 
of  the  early  hybridisers  were  so  contradictory  and 
confused — owing  partly  to  an  unfortunate  choice  of 
material  for  crossing  and  partly  to  an  unsuitable 
method  of  experiment — that  they  never  led  to  a 
consistent  point  of  view  on  which  future  progress 
could  build.  The  rediscovery  of  Mendel's  principle 
of  segregation  in  1900  therefore  marked  the  beginning 
of  an  era  in  the  study  of  heredity.  It  has  become 
progressively  clearer  that  while  mass  statistics  of 
resemblances  may  furnish  useful  information  where 
no  other  is  available,  yet  such  data  cannot  furnish 
a  basis  for  an  understanding  of  the  hereditary 
process.  The  experimental  analytical  method  is 
necessary  here,  as  in  other  fields  of  biology.  The 
results  of  the  experimental  method,  however,  can 
be  and  have  been  applied   to  genealogical  pedigrees 

of    inheritance    in    man    with    illuminating    results. 

8 

nOFERTY  LIBRARY 


THE  GENERAL  ASPECTS  OF  HEREDITY     9 

This  method  has,  of  course,  certain  definite  limitations, 
since  evidence  is  available  only  from  such  marriages 
as  have  taken  place.  But  in  many  cases  of  simple 
Mendelian  inheritance  this  evidence  is  quite  as  clear 
and  unequivocal  as  though  actual  experimental 
crosses  had  been  made  for  the  purpose  of  determining 
the  method  of  inheritance. 

The  number  of  characters  in  man  which  are  now 
known  to  follow  a  Mendelian  t^'pe  of  inheritance 
is  surprisingly  large.  It  is  therefore  desirable  to 
elucidate  briefly  the  principles  of  Mendelian  inherit- 
ance for  those  who  are  not  already  familiar  with  the 
matter.  An  elementary  treatment  of  the  subject 
is  to  be  found  in  Punnet t's  Mendelism.  While  thus 
emphasising  the  importance  of  Mendelian  heredity", 
particularly  as  regards  the  inheritance  of  abnormali- 
ties in  man,  we  wish  also  to  stress  the  value  of 
biometric  studies  of  inheritance,  for  there  are  many 
characters  in  w^hich  this  is  the  only  method  of  analysis 
which  can -be  applied.  The  two  methods  are  com- 
plementary and  are  becoming  more  and  more  closely 
interwoven  in  the  study  of  heredity.  On  the  one  hand, 
experimentalists  are  recognising  the  advantages  of 
a  mathematical  anal3^sis  of  their  results,  while  on 
the  other,  biometricians  realise  the  advantages  of 
material  under  experimental  control.  The  inter- 
action of  both  methods  produces  the  ideal  result,  but 
this  is,  of  course,  not  always  possible.  The  view 
taken  here  is  that  while  Mendelian  hereditv  is  verv 
common  in  mankind,  especially  as  regards  the  inheri- 
tance of  abnormalities,  yet  it  is  by  no  means  universal. 
Many  quantitative  characters,  and  perhaps  racial 
characters,  will  probably  be  found  not  to  follow  simple 
laws  of  inheritance  involving  fixed  germinal  units. 

As  an  example  of  Mendelian  inheritance  let  us 
consider  brachydactyly  or  short  fingers  in  man,  the 
digits  having  two  joints  instead  of  three.     This  condi- 


lo  HEREDITY  AND  EUGENICS 

tion  is  dominant  to  the  normal,  which  is  spoken 
of  as  recessive.  Brachydactylous  individuals  have 
always  married  normals.  Persons  showing  this  trait 
have  therefore  always  been  the  children  of  one  normal 
and  one  abnormal  parent.  They  are  therefore  hybrid 
or  heterozygous  in  nature  as  regards  this  character, 
and,  since  they  are  brachydactylous  in  appearance, 
this  condition  is  said  to  be  dominant  to  the  normal. 
Now  the  essential  feature  of  Mendelian  behaviour 
is  that  the  factors  or  determiners  for  such  a  pair  of 
characters  as  normal  and  brachydactylous  fingers 
separate  in  the  formation  of  the  germ  cells,  so  that 
half  the  germ  cells  of  a  brachydactylous  person 
who   had    one    normal  parent  will   carry    the    factor 

Germ  cells.  Unions  oF  Germ  cells  oF 

\        ■■'     SO  >i    B     ^.^^^  germ  cells  oFFspring. 

parent  7  """--^  ^"""--^  __— 

'  50  Z    n  ^     B(n).(50%)    — 


Normal 


n  n     (50  X) 


parent.         |  --■^.,^  ^,^--^'^  '       '    50  y.   n 


Fig.  I. — Result  of  Cross  between   Heterozygous 
Brack YDACTYL  and  a  Normal  Parent. 

for  brachydactyh'  and  half  will  carry  the  factor  for 
normal  fingers.  If  such  a  person  marries  a  normal 
individual,  all  of  whose  germ  cells  are  therefore 
carrying  the  factor  for  normal  fingers,  then,  on  the 
average,  half  the  children  will  be  brach3"dactylous 
and  half  normal,  for  the  chances  for  the  germ  cell 
matings — (i)  normal  x  normal  and  (2)  normal  X 
brachy dactyl — are  equal.  The  result  will  be  clear 
from  the  accompanying  diagram  (Fig.  i). 

Hence  we  see  that  as  long  as  matings  of  brachy- 
dactyls  wdth  normals  continue,  half  the  children  will, 
on  the  average,  be  heterozygous  brachydactyls 
(transmitting  this  character  to  half  their  offspring), 
while  the  other  half  of  the  children  will  be  pure  normal. 


THE  GENERAL  ASPECTS  OF  HEREDITY    ii 

and  transmit  only  the  normal  condition  to  all  their 
offspring.  In  other  words,  the  heterozygous  domi- 
nants will  continue  to  produce  both  types  when 
mated  to  normals,  while  the  normals  derived  from  such 
a  cross,  being  recessive,  have  entirely  lost  the  brachy- 
dactylous  condition  (or  rather  never  had  it),  and  will 
therefore  have  only  normal  offspring  even  if  two  such 
normals  from  a  brachydactylous  cross  mate  together. 
For  a  full  discussion  of  brachydactyly,  see  p.  78. 

Many  abnormalities  in  man  are  simple  dominants 
and  will  therefore  be  inherited  in  this  manner. 

In  order  to  make  clearer  the  nature  of  Mendelian 
heredity,  let  us  consider  the  other  types  of  mating 
which  commonly  occur  in  organisms  showing  a  single 


Heterozygous 
brachydactyl 
parent. 


Heterozygous 
brachydactyl 
parent. 


Germ  cells 

SO  X    B 


Fi  hybrids  (zygotes) 
25  y.     B     B 


25  y.     ..B         \75X    'l^/Xcecty, 


25  %     B     n 


25  y.     n.      n  25  y^     normal 


Fig.  2. — Results  of  Cross  between  Two  Heterozygous 

Brachydactyl  Parents. 


difference.  If  tw^o  such  individual  organisms  which 
are  pure  or  homozygous  are  crossed,  the  first  hybrid 
generation  (written  briefly  Fj)  will  show  only  the 
dominant  character.  But  if  two  of  these  F^  hybrids 
are  intercrossed,  their  offspring  will  number  on  the 
average  three  dominants  to  one  recessive.  Thus, 
in  a  marriage  between  two  heterozygous  brachy- 
dactyls,  three-fourths  of  the  children  would  be  ex- 
pected to  be  brachydactylous.  The  reason  for  this 
will  be  understood  from  the  following  diagram  (Fig.  2). 
The  four  possible  combinations  of  the  two  types 
of  germ  cells  will  occur  with  equal  frequenc}^  and 
since  the  factor  for  brachydactyly  is  absent  from  only 


12 


HEREDITY  AND  EUGENICS 


one  of  the  four  combinations,  it  follows  that  only 
25  per  cent,  of  the  offspring  will  be  likely  to  have 
normal  lingers.  Of  the  other  75  per  cent,  which  are 
brach3'dact3^1ous,  two  out  of  three  will  be  heterozygous 
{i.e.,  with  half  their  germ  cells  of  each  type),  while 
one-third  will  be  homoz^^gous,  carrying  the  determiner 
for  brach^'dactyl}'  in  all  their  germ  cells. 

We  may  similarh'  consider  the  case  where  a  hetero- 
zygous brach3'dactyl  marries  a  homozygous  brachy- 
dact\d.* 

From  the  diagram  (Fig.  3)  it  will  be  seen  that  the 
offspring  from  such  a  mating  would  be  all  brachy- 


Heberozygous 
brachydacbyl 
parent. 


Germ   cells 
50%  B 


ZvQotes 


/homozygous 

brachydacbyl 

parent. 


50%    B 


Fig.  3. — Theoretical  Results  of  Cross  between  a 
Heterozygous  and  a  Homozygous  Parent. 


dact\dous,  half  of  them  heteroz3^gous  and  half  homo- 
Z3^gous.  So  long  as  the  former  continued  mating 
wdth  homoz3^gous  brach3^dact3ds  the  normal  condition 
would  be  completeh"  suppressed,  and  the  strain  would 
appear  to  be  pure  for  brach3^dactyly.  But  if  in 
any  generation  two  heterozygous  individuals  mated, 
there  would  be  one  chance  in  four  of  the  recessive 
condition  reappearing.  The  sudden  appearance  of 
a  reversion  or  throw  back  in  a  pedigree  strain,  for 
example,  of  cattle,  is  no  doubt  often  to  be  accounted 
for  in  this  wa3^     A  recessive  character  ma3^  thus  be 

*  There  is  some  evidence  that  the  homozygous  brachy-phalan- 
gous  (related)  condition  is  non-viable  and  therefore  cannot  exist 
(see  p.  90). 


THE  GENERAL  ASPECTS  OF  HEREDITY   13 

carried  in  the  germ  plasm  of  a  strain  for  many  genera- 
tions, only  to  crop  out  again  when  a  chance  mating 
of  two  heterozygous  individuals  takes  place. 

It  is  not  known  how  or  when  brachydactyly  origi- 
nated, but  it  probably  occurred  centuries  ago,  and  pre- 
sumably arose  in  the  first  instance  as  a  mutation — i.e., 
a  sudden  and  probably  spontaneous  germinal  change.* 

Fortunately,  the  segregation  which  takes  place  in 
germ-cell  formation  can  now  be  referred  to  definite 
elements  in  the  cells — namely,  the  chromosomes. 
These  are  the  elements  of  the  nucleus  whose  con- 
stancy in  number  and  shape  for  each  species  of  animal 
and  plant  is  one  of  the  remarkable  features  of  organic 
structure.  In  the  complicated  process  of  mitotic 
nuclear  division,  w^hich  happens  whenever  cells 
divide  in  the  growth  and  development  of  the  organism, 
the  essential  fact  is  that  they  are  split  lengthwise, 
so  that  each  daughter  cell  contains  in  its  nucleus  the 
longitudinal  halves  of  every  chromosome.  Although 
these  bodies  seem  to  merge  in  the  resting  nucleus 
into  a  mass  in  which  the  outlines  of  the  separate 
chromosomes  are  lost,  yet  there  are  cases  in  which 
the  outlines  can  still  be  traced,  each  chromosome 
forming  a  separate  compartment  or  vesicle  of  the 
nucleus.  There  is  also  evidence  that  the  parts  of 
the  various  chromosomes  maintain  their  special  re- 
lationships throughout  the  period  between  one 
division  and  another  even  when  visible  boundaries 
are  lost,  or,  at  any  rate,  that  the}^  reassemble  with 
the  same  arrangement  as  they  disappeared.  There 
is  something,  not  at  present  understood,  which  main- 
tains the  unity  of  the  chromosome  as  a  persisting 
structure,  and  determines  the  constancy  of  its  relative 
size  and  shape  during  mitosis  in  the  various  parts  of 
the  organism. 

*  For  a  discussion  of  the  causes  and  nature  of  Mutation,  see 
Gates  (1915,  chap.  ix.). 


14  HEREDITY  AND  EUGENICS 

The  organism  begins  its  development  from  the 
union  of  the  nuclei  of  egg  and  sperm.  But  when 
this  union  happens  it  is  not  a  mere  interminghng 
of  two  fluid  substances,  for  the  chromosomes,  which 
are  highly  viscous  in  the  condensed  condition, 
maintain  their  separate  identity ;  and  in  the  subse- 
quent nuclear  divisions  they  frequently  arrange  them- 
selves in  pairs,  each  pair  consisting  of  one  chromo- 
some of  paternal  origin  (from  the  male  germ  cell) 
and  one  of  maternal  origin  (from  the  female  germ 
cell).  In  man}^  animals  and  plants  the  various  pairs 
are  distinguishable  from  each  other  in  size  or  shape. 
The  chromosomes  may  therefore  be  said  to  possess 
individualit}'  and  to  show  genetic  continuit}^  from 
generation  to  generation. 

When  the  germ  cells  of  an  organism  undergo 
maturation  as  the  organism  develops,  the  chromo- 
some number  in  them  is  reduced  to  one-half.  The 
essential  feature  of  this  complicated  process  is  the 
separation  of  the  pairs  of  chromosomes  which  are 
characteristic  of  the  somatic  nuclei,  so  that  the  nuclei 
of  the  eggs  and  sperms  receive  one  member  of  each 
pair  and  hence  have  half  as  many  chromosomes  as 
the  somatic  cells.*  Half  the  germ  cells  will  thus 
receive  one  member  of  each  pair,  and  half  the  other. 
This  maturation  process  has  been  studied  in  great 
detail  in  hundreds  of  plants  and  animals,  as  well  as 
in  man  (see  p.  20).  In  the  separation  of  pairs  in  the 
reduction  divisions  there  is  free  assortment  of  the 
chromosomes.  There  are  many  reasons  for  believing 
that  the  chromosomes  are  the  basis  of  Mendelian 
inheritance,  and  that  the  segregation  of  characters, 
which  IMendel's  experiments  indicated  took  place 
in  the  formation  of  the  germ  cells,  really  depends 
on  the  separation  of  the  chromosome-pairs  in  the 
reduction  divisions. 

*  Further  complications  of  this  process  need  not  concern  us  here. 


THE  GENERAL  ASPECTS  OF  HEREDITY   15 


-^t^:' 


That  segregation  of  factors  really  takes  place  during 
meiosis  (the  period  during  which  chromosome  reduc- 
tion occurs)  has  been  shown  by  the  formation  of  two 
types  of  pollen  grain  in  certain  hybrid  rice  plants.  In 
these  Fi  hybrids  half  the  pollen  grains  contain  starch 
grains,  like  the  pollen  grains  of  one  parent,  while  the 
other  half  contain  no  starch.  Fig.  4,  from  a  section 
of  an  anther  treated 
with  iodine,  shows 
the  two  types  of  pol- 
len grains  scattered 
in  equal  numbers 
through  the  anther. 

Thus  in  an  organ- 
ism which  is  hetero- 
zygous for  one  pair 
of  characters,  say 
short  hair  (domin- 
ant) or  long  "  An- 
gora "  hair  (reces- 
sive) in  guinea-pigs, 
the  Fj  hybrid  ani- 
mals will  have  short 
hair,  and  all  their 
cells  w^ill  contain  a 
pair  of  chromosomes 
which  differ  in  that 
one  chromosome 
contains  the  deter- 
miner for  short  coat, 

while  its  mate  contains  the  determiner  for  long 
coat.  When  the  germ  cells  of  this  guinea-pig  are 
formed,  this  pair  of  chromosomes,  like  the  other 
pairs,  is  separated,  and  half  the  eggs  or  sperms, 
as  the  case  may  be,  get  the  chromosome  with 
the  determiner  for  short  hair,  while  the  other  half 
receive  its  mate  containing  the  determiner  for  long 


Fig.  4. — Photomicrograph  showing 
Segregation  of  Pollen  Types  in  a 
Rice  Hybrid.   (After  F.  R.  Parnell.) 


i6  HEREDITY  AND  EUGENICS 

hair.  From  this  it  follows,  as  shown  in  the  diagram 
in  Fig.  I  (p.  lo),  that  three-quarters  of  the  individuals 
in  the  next  generation  (Eg)  will  have  short  hair,  the 
remaining  quarter  having  Angora  hair.  This  is  because 
when  the  eggs  and  sperms  unite  in  fertilisation,  half 
the  eggs  and  half  the  sperms  will  contain  the  chromo- 
some determining  short  hair,  while  the  other  half 
carry  its  mate  with  the  determiner  for  long  hair. 
The  fertilised  eggs  will  then  be  of  three  types  :  ( i )  con- 
taining a  pair  of  chromosomes,  both  of  which  carry 
the  determiner  for  short  coat.  When  these  eggs 
develop  into  organisms  which  can  be  bred  together, 
they  can  obviously  give  only  short-coated  offspring. 
They  are  homozygous  dominants.  (2)  These  ferti- 
lised eggs  will  contain  a  pair  of  chromosomes  with 
determiners  respect ivety  for  long  and  short  coat,  and, 
according  to  the  laws  of  chance  combination,  they  will 
be  twice  as  numerous  as  the  last.  They  are  the 
heteroz3^gous  dominants,  their  bodies  indistinguish- 
able from  the  pure  dominants  (when  dominance  is 
complete),  but  their  germ  plasm  as  well  as  all  their  body 
cells  containing  an  ''  unequal  "  pair  of  chromosomes 
which  will  separate  as  in  the  E^  to  produce  the  next 
generation.  These  two  classes  of  F2  animals,  together 
making  up  three-quarters  of  the  offspring,  are  visibly 
short-coated.  (3)  In  the  third  class  of  fertilised  eggs 
both  chromosomes  of  this  pair  will  contain  the 
determiner  for  long  coat.  They  will  develop  into 
long-coated  animals,  their  body  cells  and  germ  cells 
will  all  contain  the  descendants  of  this  pair  of  chromo- 
somes, and  they  wdll  give  long-coated  offspring  w^hen 
bred  together.  They  are  the  homozygous  recessives, 
and  because  they  result  from  chromosome  recom- 
binations taking  place  according  to  chance,  they 
are  as  numerous  as  the  first  class,  the  homoz^^gous 
dominants. 

The  history  of  the  chromosomes  in  organisms  was 


THE  GENERAL  ASPECTS  OF  HEREDITY   17 

worked  out  quite  independently  of  genetic  experi- 
ments, but  they  furnish  precisely  the  mechanism 
required  to  explain  Mendelian  behaviour,  although 
the  main  facts  of  their  history  were  known  before  the 
rediscovery  of  Mendel's  laws  in  1900.  The  number  of 
freely  assorting  groups  of  Mendelian  characters  in  a 
species  should  therefore  be  the  same  as  the  number 
of  pairs  of  chromosomes,  and  the  experimental  work, 
particularly  with  the  fruit  fly  Drosophila,  clearly 
indicates  that  this  is  the  case. 

Differences  in  the  chromosomes  in  crossed  races 
appear  to  determine  the  different  types  and  combina- 
tions of  characters  which  arise  in  the  offspring.  It 
thus  appears  that  Mendelian  differences  in  general 
have  originated  as  mutations,  probably  through  an 
alteration  in  a  portion  or  locus  of  a  chromosome.  That 
the  differences  which  arise  in  this  way  are  inherited 
as  Mendelian  factors  results,  then,  from  the  manner 
of  distribution  of  the  chromosomes  in  the  reduction 
divisions,  when  the  nuclei  of  the  germ  cells  are  formed. 
Mutations  seem  to  arise  in  the  germ  plasm  at  relatively 
infrequent  intervals.  They  may  then  be  handed 
down  to  later  generations  for  an  indefinite  period. 
In  some  cases  the  same  mutation  appears  indepen- 
dently more  than  once. 

Let  us  now  consider  the  inheritance  of  a  recessive 
Mendelian  character.  Feeble-mindedness  ma}'"  be 
taken  as  an  example,  for  it  appears  to  be  generally 
inherited  as  a  simple  Mendelian  recessive.  Con- 
structing a  diagram  (Fig.  5),  we  see  that  all  the 
germ  cells  of  a  feeble-minded  person  will  carry  the 
factor  for  feeble-mindedness,  since  the  character 
is  recessive. 

If  mated  with  normal,  the  children  will  all  be  normal 
for  the  same  reason,  and  the  defect  will  seem  to  have 
disappeared.  But  these  normals  will  all  be  hetero- 
zygous, carrying  the  defect  for  feeble-mindedness  in 


i8 


HEREDITY  AND  EUGENICS 


half  their  germ  cells.  If  two  such  persons  mate 
together,  it  will  be  seen  from  the  following  diagram 
(Fig,  6)  that  half  the  germ  cells  of  each  will  be  normal 
and  half  carr}-  the  defect. 

This    will    give    four    combinations    of   germ    cells 
occurring  with  equal  frequency.     Three  of  them,  or 


FeeblemindecA 
parent 


Germ   cells 
all    F 


Cro 


Normal 
parent. 


all    N 


ss 


N(F) 


Fig.  5. — Result  of  Cross  between  a  Dominant  and  a 
Recessive  Character  in  F^. 

on  the  average  three-fourths  of  the  offspring,  will 
be  normal,  the  other  fourth  will  be  feeble-minded. 
Moreover,  of  the  normals  tw^o-thirds  will  be  carrying 
feeble-mindedness  as  a  recessive  character  while  the 
other  third  will  be  untainted.      Further,  it  is  clear 


Heterozygous 
parents. 

Germ  cells. 

^        50  %   N 

N(F)    <; 

~-^        50  %    F 

^        50  %    N 

Unions  oF  germ  cells. 
25  X  N  N 

25  %  N  F 

25  %  N  F 


^  (F)    ^^  ^^^"'^_— — ^^   25  %  r  F 


50  %    F 
Fig.  6. — Results  of  above  Cross  in  F., 


that  if  the  Mendelian  behaviour  is  strictly  adhered 
to  two  feeble-minded  parents  can  have  only  feeble- 
minded offspring.  The  exceptions  to  this  rule,  if 
they  exist,  are  so  few  as  to  be  negligible.  For  a  further 
account  of  feeble-mindedness  see  p.  149. 

There  is  no  doubt  that  the  germ  plasm  of  any  human 


THE  GENERAL  ASPECTS  OF  HEREDITY   19 

strain  contains  numbers  of  such  recessive  characters, 
which  may  be  transmitted  for  generations  without 
appearing,  until  union  with  an  individual  carrying 
the  same  recessive  character  may  ultimately  bring 
it  out  in  some  (25  per  cent.)  of  the  offspring.  The 
presence  of  similar,  undesirable  recessive  characters 
in  the  germ  plasm  is  thus  the  chief  danger  from 
inbreeding  or  intermarriage  of  cousins.  The  main 
features  of  a  recessive  character  are,  then,  that  it 
disappears  in  the  first  generation  of  a  cross  between 
a  pure  dominant  and  a  pure  recessive,  while  it  re- 
appears in  about  one-quarter  of  the  offspring  of  two 


Germ  cells    X 


XX  XY 


Fig.  7. — Diagram  to  show  the  History  of  the  Sex 

Chromosomes. 

individuals  heterozygous  for  the  character.  It  will 
appear  in  about  half  the  offspring  of  matings  between 
a  heterozygous  normal  and  a  (pure)  recessive. 

Another  type  of  Mendelian  character,  which  in  its 
inheritance  follows  exactly  the  distribution  of  the  sex 
chromosomes,  is  known  as  sex-linked  inheritance. 
Such  characters  evidently  depend  for  their  origin 
upon  mutations  occurring  in  the  sex  chromosomes. 
As  an  example  of  this  in  man  we  may  consider  colour- 
blindness. The  nature  of  this  inheritance-mechanism 
will  be  clear  from  the  following  diagram  (Fig.  7), 
showing  the  history  of  the  sex  chromosomes  as  they 
appear  to  behave  in  man. 


20  HEREDITY  AND  EUGENICS 

The  history  of  the  sex  chromosomes  has  been  clearly 
shown  in  many  animals,  and  in  the  fruit  fly  Drosophila 
a  large  number  of  sex-linked  mutations,  determined 
apparently  by  changes  in  loci  of  the  X-chromosome, 
have  been  studied. 

A  brief  account  is  first  necessary  of  the  sex 
chromosomes  as  they  apparently  exist  in  man. 
Although  many  observations  have  been  made  on  the 
subject,  the  facts  are  not  3'et  known  with  certainty; 
but  the  details  are  gradually  becoming  clear.  It 
appeared  at  one  time  that  the  negro  had  24  chromo- 
somes and  the  white  man  48,  but  this  apparent 
difference  ma}^  have  been  due  to  clumping  of  the 
chromosome  pairs  in  the  process  of  fixation,  so  that 
they  looked  like  single  chromosomes.  Also  in  the 
earlier  accounts  one  or  two  more  chromosomes  were 
found  in  the  female  than  in  the  male,  but  later  investi- 
gators are  agreed  that  there  is  a  pair  (XY)  of  sex 
chromosomes  which  are  distinguishable  b}^  their  shape 
and  behaviour  from  the  other  chromosomes.  It 
appeared  from  the  studies  of  Guyer  (1910,  191 4) 
and  of  Montgomery  (191 2)  on  human  spermato- 
genesis that  the  male  negro  possesses  22  chromosomes, 
including  2  sex  or  accessory  chromosomes.  Mont- 
gomery found  that  the  accessories  were  irregularly 
distributed  in  the  reduction  divisions.  It  was  inferred 
that  the  female  number  was  24.  Von  Winiwarter 
(191 2),  however,  studying  members  of  the  white  race, 
found  47  chromosomes  in  man  and  48  in  woman 
(oogonial  divisions).  Farmer,  Moore  and  Walker 
(1906),  in  examining  pathological  tissue  (somatic  cells) 
presumably  of  white  people,  found  usually  32  chromo- 
somes, while  Wieman  (191 3)  counted  33  to  38  chro- 
mosomes in  a  human  embr3^o  the  parentage  of  which 
is  not  stated.  More  recently  Wieman  (191 7)  de- 
scribes human  spermatogenesis  with  24  chromosomes 
in  both  negro  and  white,  including  an  XY  pair  of  sex 


THE  GENERAL  ASPECTS  OF  HEREDITY   21 

chromosomes  which  divide  in  the  first  reduction 
division  and  segregate  in  the  second,  unUke  the  other 
chromosomes  which  segregate  in  the  first  and  divide 
in  the  second.  Still  more  recently,  Painter  (1921), 
in  a  preliminary  account  of  spermatogenesis  in  both 
whites  and  negroes  from  Texas,  finds  approximately 
48  chromosomes  in  both,  including  an  XY  pair  of 
sex  chromosomes.  This  is  a  partial  confirmation  of 
Von  Winiwarter.  It  might  appear  that  all  these 
investigators  were  right  in  their  determinations  of 
numbers,  and  that  human  individuals  exist  with 
24  (2X  or  diploid),  about  36  (3X  or  triploid),  and  48 
(4X  or  tetraploid)  chromosome  numbers.  The  chro- 
mosomes of  all  mammals  are,  however,  notoriously 
difficult  to  deal  with,  and  it  seems  more  likely  that 
clumping  may  have  given  rise  to  an  appearance  of 
lower  numbers.  The  existence  of  triploid  and  tetra- 
ploid races  of  mankind  would,  however,  be  in  accord 
with  their  occurrence  in  man}^  species  of  plants  and 
animals  (see  Gates,  191  5,  pp.  195  ff.).  In  an}^  case, 
it  seems  clear  that  the  higher  number  (48)  of  chromo- 
somes is  present  at  least  in  some  men,  and  that  an 
XY  pair  of  chromosomes  exists  in  the  male. 

It  may  be  pointed  out  that  the  number  48  is  a  rather 
high  one,  and  is  approximately  double  the  number 
found  in  some  mammals.*  It  has,  therefore,  probably 
originated  at  some  time  by  sudden  doubling  of  the 
chromosome  number,  as  this  was  originally  shown 
to  take  place  when  CEnothera  gigas  appears  as  a 
mutation  from  CE.  Lamarckiana  (see  Gates,  191 5, 
pp.  118,  209).  Whether  this  doubling  to  produce 
48  chromosomes  occurred  in  some  of  the  races  of 
mankind,  or  earlier  in  his  ancestry,  remains  to  be 
determined.  In  the  matter  of  relationships  and 
phylogeny,  as  has  recently  been  shown,  in  the  varieties 

*  Painter  (1922)  reports  finding  54  chromosomes,  including 
an  XY  pair,  in  a  ring-tail  monkey. 


22  HEREDITY  AND  EUGENICS 

of  wheat,  and  in  a  number  of  other  instances,  the 
determination  of  chromosome  numbers  and  shapes  is 
of  great  value. 

Returning  to  the  question  of  human  chromosomes, 
there  are  many  difficulties  attending  their  study,  so 
that  neither  their  total  numbers  nor  the  behaviour 
of  the  sex  chromosomes  can  be  regarded  as  settled. 
Von  Winiwarter  found  an  unpaired  X  chromosome 
in  the  male,  while  later  workers  are  agreed  in  finding 
an  XY  pair.       In  either  case,  the  mechanism  of  sex 
determination    and    the    inheritance    of    sex  -  linked 
characters  is  essentially  the  same,  so  it  will  be  assumed 
that  the  later  work  is   correct    in  describing  an  XY 
pair.     This  type   of  sex -determining   mechanism   is 
well  known  in  some  of  the  insects.     It  may  be  briefly 
described   as    follows    (see    Fig.    8).     Males    have   an 
unequal  XY  pair  of  sex  chromosomes,  the  X  usually 
being  larger  than  the  Y,  while  females  have  a  pair 
of  X   chromosomes   (XX).     In   the   spermatogenesis 
of  the  male,  the  X  passes  undivided  into  half  the 
sperm,  w^hile  the  other  half  receive  the  Y.     Since  the 
females  have  a  pair  of  X  chromosomes,  all  the  eggs 
before  fertilisation  will  contain  one  X.     In  fertilisa- 
tion there  is  an  equal  chance  that  a  sperm  containing 
an  X  will  enter  an  egg,  and  produce  a  female,  or,  that 
a  sperm  bearing  a  Y  will  function  and   so  produce 
a  male.     Through  this  general  mechanism  an  approxi- 
mation to  equality  of  the  sexes  is  maintained.     But 
it  is  now  known  that  there  are  various   conditions 
which  may  come  in  to  disturb  this  tendency  to  equality 
in  numbers  of  the  sexes. 

We  are  now  in  a  position  to  understand  the 
mechanism  of  inheritance  of  sex-linked  characters, 
such  as  colour-blindness,  in  man. 

The  diagram  shows  only  the  sex  chromosomes, 
which  are  XX  in  the  female  and  XY  in  the  male. 

The    underlined    X    is    carrying    the     factor     for 


THE  GENERAL  ASPECTS  OF  HEREDITY  23 

colour-blindness.  The  male,  XY,  would  therefore  be 
colour-blind.  Mated  with  a  normal  woman,  their 
male  children  would  all  be  normal.  The  X  chromo- 
some of  the  father,  however,  goes  to  all  his  daughters, 


Parents 


XX 


X  Y 


Germ  cells 


XX      X  Y 


Zygotes 


XX      XYcf 


OXX 


Germ  cells 


XX       XY 


Zygotes  OXX       OXX        XYCJ"    XYd' 


Germ  cells 


XX 


XY 


Zygotes 


^XX       XX^       XYC?      XYC/ 


Fig.   8. — Diagram   to  illustrate  the   Inheritance   of   Sex- 
Linked  Characters  through  the  X-Chromosome. 


who  are  all,  therefore,  transmitters  of  the  defect  to 
future  generations.  With  a  husband  who  is  normal, 
they  will  transmit  the  defect  to  half  their  children 
of  both  sexes,  as  shown  in  the  next  two  lines  of  the 


24  HEREDITY  AND  EUGENICS 

diagram  (Fig.  8),  but   onl}'  the  sons   will  be   colour- 
blind. 

The  last  three  lines  show  how  a  colour-blind  father 
and  a  heteroz3'gous  mother  will  have  a  family  in  which 
half  the  daughters  show  the  defect  and  half  the  sons 
will  show  it.*  If  the  mother  were  homozygous  for 
colour-blindness  and  the  father  also  carried  it,  then 
all  the  children  would  be  colour-blind.  There  is  no 
instance  of  a  colour-blind  father  transmitting  the 
condition  to  the  next  generation,  except  in  connec- 
tion with  a  mother  who  transmits  it.  This  criss- 
cross type  of  inheritance  is  more  complicated  than 
simple  Mendelian  behaviour  in  which  both  parents 
take  the  same  part  in  inheritance,  but  it  is  simply 
explained  by  assuming  the  behaviour  to  be  due  to  the 
transmission  of  a  defective  X  chromosome. 

It  appears,  then,  that  in  all  these  cases  the  fact 
that  the  differences  are  inherited  as  Mendelian  factors 
results  from  the  manner  of  distribution  of  the  chro- 
mosomes in  the  reduction  divisions  at  the  time  the 
germ  cells  of  the  organism  are  matured.  It  may  be 
that  some  of  the  fundamental  resemblances  betw^een 
related  organisms  are  inherited  in  a  different  wa}^ 
Since  in  experimental  breeding  it  is  only  possible 
to  study  directl}^  the  inheritance  of  differences, 
evidence  concerning  the  process  of  inheritance  of 
resemblances  must  necessarily  be  indirect  and  closel}' 
wrapped  up  with  development  itself. 

We  ma}^  now  consider  some  of  the  differences 
appearing  in  man  which  so  often  follow  one  of  these 
types  of  Mendelian  behaviour.  While  dominance 
is  very  common,  especiall}^  in  connection  with  abnor- 
malities, it  is  not  by  any  means  universal.  There 
is,  for  instance,  no  dominance  in  such  a  character 
as  skin  colour,  but  the  first  generation  is  intermediate 

*  There  appear  to  be  some  irregular  cases  in  which  colour- 
bhndness  shows  in  a  heterozygous  woman. 

fnffparr  librart 

19,  C.  Statt  Colkj^ 


THE  GENERAL  ASPECTS  OF  HEREDITY  25 

and  back-crosses  will  further  dilute  the  colour.  It  is 
probable  that  in  organisms  at  large  complete  domi- 
nance is  the  exception  rather  than  the  rule.  Why 
dominant  mutations  should  be  so  numerous  in  man 
is  at  present  quite  unexplained.  In  Drosophila, 
only  about  a  dozen  dominant  mutations  have  ap- 
peared among  some  300,  all  the  rest  being  recessive, 
and  they  are  equally  uncommon  in  other  organisms. 

The  biological  characters  or  differences  observable 
in  the  human  race  and  for  the  most  part  inherited 
include  not  merely  the  more  striking  racial  divergen- 
cies, but  also  the  innumerable  structural  and  mental 
or  temperamental  differences  that  we  see  in  the 
individuals  of  any  population,  however  "  pure  "  the 
race.  Colour  of  hair  and  eyes,  height  and  size  of 
various  parts  of  the  body  (for  there  is  some  evidence 
that  these  may  be  independently  inherited  for  different 
segments),  conformation  of  the  head  and  features, 
size  and  shape  of  eyes,  e-ars,  nose,  mouth,  hands,  and 
feet — there  is  good  reason  to  believe  that  the  element 
of  inheritance  enters  largely  into  the  perpetuation 
of  a  host  of  such  differences  as  well  as  others  more 
minute.  Everyone  can  cite,  from  his  own  experi- 
ence, cases  of  such  essentially  phj^siological  traits  as 
longevity  and  early  baldness*  or  greyness  "running 
in  families." 

*  In  an  interesting  study  of  the  inheritance  of  baldness,  by 
Dorothy  Osborn  (1916),  she  tabulated  the  results  for  twenty-two 
families  and  reached  definite  conclusions.  Baldness  is  found  to 
be  a  sex-limited  trait,  being  inherited  as  a  dominant  character 
from  father  to  son.  In  the  woman  it  acts  as  a  recessive,  and 
may  be  transmitted  as  such,  only  appearing  as  baldness  when 
present  in  the  duplex  (homozygous)  condition.  This  may 
explain  the  greater  rarity  of  baldness  in  women.  Baldness  is 
frequently  associated  with  progressive  decrease  in  the  concentra- 
tion of  thyroid  in  the  blood  (see  pp.  211  ^.).  This  view  of  early 
baldness  as  a  sex-limited  trait  is  borne  out  by  data  of  Sedgwick 

(1863). 

It  is  interesting  to  note  in  this  connection  that  Duerden  (191 8, 


26  HEREDITY  AND  EUGENICS 

Differences  in  reactions  to  serums  and  to  various 
diseases,  as  well  as  other  evidence,  indicates  the 
existence  of  corresponding  chemical  and  constitutional 
differences  between  individuals.  The  inheritance  of 
such  differences  is  now  commonly  recognised.  Only 
a  few  years  ago,  in  the  Law  Courts,  the  disposal  of  a 
large  estate  turned  upon  a  peculiar  conformation 
of  the  ear  occurring  in  the  father  and  the  supposed 
son.* 

A  considerable  bod}^  of  detailed  evidence  concerning 
heredity  in  man  has  accumulated  in  recent  years. 
It  is  not  my  purpose  to  attempt  anything  like  a 
complete  citation  of  this  work,  but  it  may  be  of 
interest  to  enumerate  some  of  the  studies  which  have 
been  made  on  this  subject;  for  our  knowledge  of 
the  inheritance  both  of  normal  and  abnormal  traits 
in  man  must  always  form  the  chief  basis  for  eugenic 
action. 


1919)  has  shown  that  in  crosses  between  the  North  African  and 
South  African  ostrich  the  bald  spot  of  the  former  behaves  as  a 
simple  dominant  character  not  sex-linked.  In  the  chicks  the 
head  is  covered  with  a  bristly  down,  but  in  the  North  African 
birds  this  gradually  falls  out  during  the  first  few  months  and  is 
not  replaced  by  feathers. 

*  On  the  other  hand,  a  case  is  cited  (Jenks,  1916),  with  some 
evidence  of  authenticity,  in  which  a  girl  of  Swedish  ancestry, 
whose  ancestors  of  both  sexes  had  been  accustomed  for  many 
generations  to  wear  earrings,  was  born  with  a  hole  in  the  proper 
position  in  each  ear-lobe.  That  such  cases  of  inheritance  of  a 
mutilation  are  admittedly  rare  does  not  necessarily  prove  that 
they  are  non-existent.  The  fact  that  (Windle,  1891)  a  fissure 
sometimes  occurs  in  the  sulcus  intertragicus  of  the  ear,  as  an 
arrest  of  development,  scarcely  seems  an  adequate  explanation 
of  the  above  case;  but  in  an  instance  cited  by  Windle  where  the 
mother  tore  the  lobule  of  her  left  ear  when  eight  years  old,  and 
afterwards  had  eight  children,  one  of  whom,  a  boy,  had  cleft  lobule 
of  the  left  ear,  there  is  obviously  no  inheritance  involved. 


CHAPTER  III 

INHERITANCE  OF  PHYSICAL  CHARACTERS 

IN  MAN 

Stature 

Two  of  the  earliest  subjects  studied  in  connection 
with  human  heredity  were  naturally  enough  stature 
and  eye-colour.  Galton  dealt  with  these  traits  in  his 
Natural  Inheritance.  I  have  pointed  out  elsewhere 
(191 4)  that  Galton  was  a  believer  both  in  continuity 
and  discontinuity  in  variation,  and  also  in  alterna- 
tive as  well  as  blended  inheritance.  His  point  of 
view  with  regard  to  the  inheritance  of  these  two 
characters  may  be  well  illustrated  by  a  quotation 
from  Natural  Inheritance  (p.  138):  "Stature  and 
eye-colour  are  not  different  as  qualities,  but  they 
are  more  contrasted  in  hereditary  behaviour  than 
perhaps  any  other  common  qualities.  Parents  of 
different  statures  usually  transmit  a  blended  heritage 
to  their  children,  but  parents  of  different  eye-colour 
usually  transmit  an  alternative  heritage."  He  also 
remarks  (p.  139),  "  The  blending  in  stature  is  due 
to  its  being  the  aggregate  of  the  quasi-independent 
inheritance  of  many  separate  parts,  while  e3^e-colour 
appears  to  be  much  less  various  in  its  origin."  In- 
stead of  Galton's  conception  of  particulate  inheritance, 
we  now  think  in  terms  of  such  abstractions  as  multiple 
allelomorphs  or  multiple  factors.  But  this  conclusion 
of  his  concerning  stature  has  been  supported  by 
Davenport  (191 7),  who  concludes  from  a  considerable 
aggregation    of   analysed    data   that    the   correlation 

between  "  knee  height  "  and  "  pubic  arch  minus  knee 

27 


28  HEREDITY  AND  EUGENICS 


* 


height  "  or  length  of  thigh,  is  only  24  per  cent.*^ 
Knee  height  includes  height  of  ankle,  which  is  con- 
sidered an  independent  variable.  The  correlation 
between  supra-pubic  and  sub-pubic  portions  of 
stature  is  found  to  be  30  per  cent.,  and  striking  differ- 
ences in  the  relative  lengths  of  these  portions  of  the 
bod}'  occur  in  different  races  of  man.  Thus  Eskimo, 
Mongoloids,  and  some  American  Indian  tribes  have 
a  relativel}^  long  trunk  and  short  legs,  while  the 
Australian  aborigines  and  some  negro  groups  have  a 
short  trunk  and  long  legs.  Of  the  supra-pubic 
region,  the  supra-sternal  or  head  and  neck,  and  sub- 
sternal or  trunk  portion,  are  independent  variables 
as  regards  length,  with  a  correlation  between  them 
of  onh'  9  per  cent.  A  defect  in  these  data  is,  however, 
the  use  of  "  sitting  height  "  as  a  measurement,  and 
the  deduction  of  certain  elements  of  the  stature  from 
that. 

Thus,  while  inherited  general  growth  factors,  such 
as  differences  in  the  amount  of  secretion  of  various 
glands,  are  concerned  in  determining  the  adult  stature 
as  a  whole,  other  factors  are  believed  to  control  inde- 
pendently the  length  of  the  various  segments  which 
go  to  make  up  stature.  Hence,  according  to  this  view, 
an  individual  ma}"  be  tall  because  of  the  presence 
of  general  growth  factors,  or  because  he  happens  to 
have  inherited  length  in  each  segment  of  his  stature. 
If  this  is  true,  then,  of  the  four  segments  that  combine 
to  form  the  total  stature,  any  individual  may  be 
long  in  some  and  short  in  others.  It  is  commonly 
stated  that  certain  families  have  predominantly 
long  trunks  and  short  legs,  while  others  may  have 
short,   stocky   trunks   combined   with   long   or   short 

*  The  calculation  of  the  length  of  different  segments  of  the 
body  by  this  indirect  method  introduces  sources  of  error,  as  Castle 
points  out,  which,  at  any  rate,  weaken  Davenport's  conclusions 
regarding  the  inheritance  of  stature. 


PHYSICAL  CHARACTERS  IN  MAN  29 

legs.  A  child  may  happen  to  inherit  all  the  relatively 
long  or  short  segment-lengths  of  its  two  parents,  and 
may  thus  be  considerably  taller  or  shorter  than  either 
parent.  Thus  uniformity  is  not  to  be  expected  in 
marriages  between  tall  and  short  people.  I  know 
personally  of  two  cases  of  marriages  between  a  very 
exceptionally  tall  man  and  an  exceptionally  short 
woman.  In  one  case  the  son  is  tall,  though  not  so 
tall  as  his  father.  In  the  other,  the  son  is  exception- 
ally short,  like  his  mother. 

Castle  (1922)  has  recently  criticised  these  con- 
clusions of  Davenport.  He  made  a  study  of  size 
inheritance  in  crosses  between  large  and  small  varieties 
of  rabbits  and  found  the  F^  generations  intermediate 
between  the  parental  races,  but  nearer  the  size  of  the 
larger  parent  owing  to  heterosis  or  hybrid  vigour. 
The  latter  phenomenon  is  well  known.  It  is  largely 
confined  to  the  F^  of  both  plant  and  animal  hybrids, 
and  probably  occurs  also  in  some  first  generation 
crosses  of  man.*  Castle  found  that  in  crosses  between 
two  small  varieties  of  rabbits,  such  as  Polish  and 
Himalayan,  the  F^  was  larger  than  either  parent 
owing  to  this  "  hybrid  vigour,"  but  the  effect  was  lost 
in  the  F2,  which  was  strictly  intermediate  in  average 
size.  In  crosses  of  either  of  these  races  with  the 
much  larger  Flemish  rabbit,  the  average  size  of  the 
F2  was  strictly  intermediate,  but  the  range  of  varia- 
tion was  much  greater  than  in  F^.  By  the  application 
of  statistical  methods  it  was  estimated  that  eight  or 
ten  independent  factors  or  linkage-systems  affected 
the  size. 

Extensive  measurements  were  made  of  weight, 
ear-length,  and  the  dimensions  of  several  bones.  A 
study  of  the  correlation  between  these  measure- 
ments   was    made,    in    order   to    determine   whether 

*  For  a  discussion  of  heterosis  in  hybrids  see  East  and  Jones 
(1919)- 


30  HEREDITY  AND  EUGENICS 

independent  factors  govern  the  size  in  different  parts 
of  the  bod}'.  The  correlation-coefficients  obtained 
were  uniformly  high,  and  Castle  reaches  the  conclusion 
that  "  the  genetic  agencies  affecting  size  in  rabbits 
are  general  in  their  action,  influencing  in  the  same 
general  direction  all  parts  of  the  body." 

This  important  contribution  of  Castle  to  the  subject 
of  size-inheritance  seems  to  indicate  that,  in  so  far  as 
rabbits  are  concerned,  there  is  no  certain  evidence  of 
factors  independently  influencing  the  size  of  particular 
organs.  Castle  applies  the  same  views  to  mammals 
and  man,  but  not  to  plants  where  "  hormone  action 
is  less  in  evidence."  He  regards  the  view  of  the 
genetic  independence  in  size  of  the  various  parts  of 
the  body  as  a  "  sporadic  relapse  into  preformation- 
ism,"  and  denies  that  any  lack  of  co-ordination  of 
organs,  such  as  Davenport  has  suggested,  can  arise 
through  the  crossing  of  different  races  of  man.  He 
points  out  also,  that  the  measurements  used  by 
Davenport  were  not  sufficiently  precise  to  give  reliable 
correlation-coefficients,  and  criticises  the  photographs 
of  a  Dinka  negro  and  a  Chiriguan  Indian  as  evidence 
that  length  of  legs  and  trunk  is  independently 
inherited.  Castle  suggests  that  there  is  the  same 
difference  in  proportions  between  a  boy  and  a  man 
as  between  the  Chiriguan  Indian  and  the  Dinka 
negro,  and  that  the  latter,  therefore,  merely  repre- 
sents a  later  stage  of  development.  He  believes 
that  Southern  Italians  are  short  of  stature  and  short- 
limbed  because  they  cease  to  grow  early,  while  Swedes 
and  Scotch  are  tall  and  long-limbed  because  they 
mature  later,  in  the  same  way  that  Flemish  rabbits 
are  large  and  have  long  ears  because  of  their  late 
maturity.  Davenport  also  recognises  general  growth 
factors,  and  it  is  evident  that  the  last  word  has  not 
yet  been  said  on  this  important  subject.  What  is 
required  is  a  mass  of  more  accurate  measurements. 


PHYSICAL  CHARACTERS  IX  MAN  31 

Two  earlier  studies  by  Punnett  and  Bailey  (191 4, 
191  8)  on  the  inheritance  of  weight  in  poultry  and  in 
rabbits  also  bear  directly  on  this  question.  They 
crossed  Gold-pencilled  Hamburgs  with  Silver  Sea- 
bright  Bantams.  The  F^  was  not  quite  so  large  as 
the  larger  parent,  while  in  F,  and  F3  the  range  of 
variation  is  beyond  that  of  either  parent — i.e.,  both 
larger  and  smaller  birds  w^ere  obtained.  The  results 
were  explained  on  the  assumption  that  four  factors 
affecting  weight  were  present,  two  of  them  being 
assumed  to  give  an  increase  of  38  per  cent,  in  a 
single  dose  or  61  per  cent,  when  present  in  the  homo- 
zygous condition.  The  other  two  factors  were 
assumed  to  give  25  per  cent,  increase  in  weight  in 
the  simplex  condition,  and  30  per  cent,  in  the  duplex 
condition.  The  results  are  believed  to  give  a  clear 
indication  that  weight  in  poultr}^  may  depend  on  the 
presence  of  definite  segregating  genetic  factors,  and 
it  is  suggested  that  the  increased  size  of  some  hybrids 
is  not  due  to  hybrid  vigour,  but  to  the  bringing  to- 
gether of  independent  growth  factors. 

In  their  later  study  of  weight  in  rabbits,  Punnett 
and  Bailey  (191 8)  made  crosses  between  the  large 
Flemish  rabbit  and  a  mixed  strain  of  Himalayan- 
Dutch-Havana  of  nearly  uniform  size.  They  also 
made  certain  crosses  betw^een  Flemish  and  Polish 
rabbits.  After  making  a  careful  study  of  the  curves 
of  growth  in  these  rabbits,  they  conclude  that  "  though 
animals  belonging  to  large  breeds  may  mature  more 
slow^ly  than  those  belonging  to  small  breeds,  it  does  not 
follow  that  age  of  maturity  is  closely  correlated  with 
size."  The  very  small  Polish  rabbit  is  believed  to 
mature  a  good  deal  more  slowly  than  a  larger  form  such 
as  the  Dutch,  and  the  conclusion  is  reached  that  size 
and  early  maturit}'  are  to  some  extent  transmitted 
independently.  These  conclusions  are  contrary  to 
the  view  of  Castle,  who  finds,  from  a  stud}'  of  growth- 


32  HEREDITY  AND  EUGENICS 

curves  in  pure  and  hybrid  races,  that  in  PoHsh  rabbits 
"  the  initial  weight  is  less,  the  growth-rate  lesS; 
and  the  completion  of  growth  comes  earlier,"  all 
these  features  combining  to  produce  a  smaller  rabbit. 
It  is  evident  from  these  and  other  contradictory 
results  that  further  studies  of  size  inheritance  in 
relation  to  rate  of  growth,  etc.,  are  necessar}-  before 
any  final  conclusion  can  be  reached;  but  it  is  highly 
probable  that  the  same  laws  of  size  inheritance  apply 
to  man  as  to  mammals,  whatever  those  laws  may  be.* 
Castle's  data  provide  strong  evidence  that  in  the 
strains  of  rabbits  he  studied  general  growth  factors 
preponderated  over  any  factors  affecting  only  the  size 
of  certain  parts.  Nevertheless,  the  effects  of  a  genetic 
factor  are  frequently  confined  almost  entirely  to  one 
organ,  and  we  see  no  reason  why  this  should  not  apply 
to  size  factors  as  well  as  others.  Wright  (191 8)  in 
a  statistical  analysis  of  earlier  measurements  by 
Castle,  of  a  stock  of  rabbits  w^hich  gave  strikingly 
high  correlations  between  skull  and  leg  measure- 
ments, brings  out  correlations  which  ''  suggest  the 
existence  of  growth  factors  w^hich  affect  the  size  of 
the  skull  independently  of  the  body,  others  which 
affect  similarly  the  length  of  homologous  long  bones 
apart  from  all  else,  and  others  which  affect  similarly 
bones  of  the  same  limb."  The  five  measurements 
considered  were  length  and  breadth  of  skull,  length 
of  humerus,  femur,  and  tibia.  Analysis  of  the  rela- 
tions shows  that  in  a  population  of  rabbits  most 
of  the  differences  between  individuals  are  those 
which  involve  the  size  of  the  body  as  a  whole.  But 
there  is  a  certain  amount  of  variation  of  each  bone 
length  independently  of  all  others  measured.  There 
are  also  groups  of  bones,  which  vary  together  inde- 

*  There  is  much  evidence  in  man  (see  p.  212)  that  the  activities 
of  various  ductless  glands,  such  as  the  thyroid  and  pituitary, 
control  the  size  and  development. 


PHYSICAL  CHARACTERS  IN  MAN         33 

pendently  of  the  rest  of  the  skeleton .  Two  such  groups 
are  skull  length  and  breadth  and  the  three  leg  bones. 
Again,  femur  and  tibia  form  a  group  subject  to 
common  influences  which  do  not  affect  the  humerus 
(foreleg).  How  far  these  variations  were  controlled 
by  genetic  factors  is  of  course  unknown. 

Castle  specifically  confines  to  animals  his  view  that 
all  size  factors  are  general,  excluding  it  from  plants 
on  the  ground  of  a  greater  hormone  control  in  animals. 
But  the  apparent  difference  may  simply  be  due  to 
the  present  state  of  our  knowledge.  In  plants  it 
has  been  shown  (Gates,  191 7)  that  when  a  large- 
flowered  species  is  crossed  with  a  small-flowered  one, 
an  intermediate  F^  ma}"  be  followed  by  later  genera- 
tions in  which  widely  different  sizes  of  flower  occur 
simultaneously  on  the  same  plant,  and  even  different 
lengths  of  petal  in  the  same  flower.  This  striking 
result,  which  has  been  studied  on  a  large  scale  in 
CEnothera  crosses,  shows  that  in  plants,  at  any  rate, 
organs  of  widely  different  size  ma}"  occur  on  the  same 
individual  as  the  result  of  inherited  differences. 

Another  important  fact  which  bears  on  the  whole 
theory  of  multiple  factors  in  the  interpretation  of 
size  inheritance  has  been  brought  out  by  Sumner 
and  Huestis  (1921).  From  extensive  measurements 
of  the  right  and  left  mandibles,  femurs,  and  pelvic 
bones  of  the  Californian  deer  mouse,  Peromysciis 
maniculatiis ,  they  have  constructed  curves  for  the 
sinistro-dextral  ratio  for  each  bone — i.e.,  the  relative 
lengths  of  the  corresponding  right  and  left  bones. 
The  range  of  variation  on  either  side  of  equality  in 
this  ratio  is,  of  course,  small  in  every  case,  but  they 
are  able  to  show  statistically  that  the  difference — 
i.e.,  excess  of  length  or  weight  on  the  right  or  left 
side — is,  as  might  be  expected,  not  inherited  from  one 
generation  to  the  next.  Nevertheless,  if  pure  races 
are  compared  with  hybrids,  the  Y^  generation  shows 

3 


34  HEREDITY  AND  EUGENICS 

a  considerable  increase  in  the  variability  of  these 
ratios.  The  authors  rightly  insist  that  this  increased 
variability  of  the  Eg  in  characters  which  are  demon- 
strably non-hereditar}^  weakens  very  much  the  force 
of  the  evidence  usually  offered  in  favour  of  the 
hypothesis  of  multiple  factors  in  size  inheritance. 
An  increased  range  of  variation  in  Eg  hybrids  cannot 
therefore  in  itself  be  accepted  as  evidence  of  the 
inheritance  of  multiple  size  factors.  In  the  light  ol 
these  results,  the  whole  subject  of  size  inheritance 
takes  on  new  aspects  and  will  require  more  critical 
re-examination . 

As  regards  human  dwarfs,  they  ma}^  be  achondro- 
plasic* — having  short  legs  and  long  trunk — or  ate- 
liotic,t  with  normal  proportions  and  reduced  size 
(miniatures).  The  former  condition  frequently  skips 
a  generation,  and  its  heredity  is  uncertain,  but  it 
appears  to  be  connected  with  derangements  of  the 
internal  secretions.  A  number  of  pedigrees  of  both 
types  of  dwarfs  are  described  in  the  Treasury  of 
Natural  Inheritance  (Pearson). 

Rischbieth  and  Barrington  (191 2)  have  accumu- 
lated an  enormous  amount  of  information  regarding 
dwarfism  in  the  human  race,  with  a  number  of  pedi- 
grees of  its  inheritance.  Regarding  achondroplasia, 
the  condition  ma}'  appear  ''  accidentally  "  or  it  may 
be  hereditar}'.  Cases  are  known  in  which  normal 
and  achondroplasic  babies  occur  in  the  same  twin 
birth.  The  condition  appears  more  commonl}'  in 
girls  than  in  bo3'S,  Kassowitz  finding  twenty-five 
girls  and  four  bo3's  in  a  total  of  twenty-nine  cases. 
An  achondroplasic  mother  may  have  children  like 
herself  or  normal,  and  delivery  must  be  b}"  Csesar- 
otomy. 

*  Achondroplasia  is  a  defect  in  the  iormation  of  cartilage  at 
the  epiphyses  on  the  ends  of  the  long  bones,  producing  dwarfs, 
t  Ateliosis  is  arrest  of  development  before  it  is  complete. 


PHYSICAL  CHARACTERS  IX  MAN         35 

Ateliosis  or  true  dwarfism  is  considered  to  be  rather 
rare.     It  is  probably  due  to  a  defect  of  the  pituitary. 

There  is  a  fair  number  of  cases  recorded  in  which 
offspring  have  been  born  to  parents  one  or  both  of 
whom  were  ateliotic.  These,  however,  with  the 
exception  of  the  cases  quoted,  have  grown  to  a  normal 
size,  if  the}^  survived  to  adult  years."  Usualh'  the 
condition  is  found  in  only  one  generation.  In  an 
exceptional  case,  an  achondroplasic  mother  produced 
an  ateliotic  son  by  an  ateliotic  father.  In  another 
case,  ateliosis  occurred  in  father  and  son,  and  probably 
in  the  grandfather. 

A  condition  in  plants,  which  appears  to  correspond 
with  achondroplas}^,  has  been  described  in  cotton, 
under  the  name  brachysm  (Cook,  191  5).  It  consists 
in  a  great  shortening  of  the  internodes  without  any 
corresponding  reduction  in  the  diameter  or  in  the 
size  or  number  of  other  organs.  This  condition  exists 
in  the  "  bush  "  varieties  of  various  vegetables  and 
cereals  such  as  beans  and  peas,  tomatoes,  oats  and 
w^heat.  Kempton  (1921)  has  studied  it  in  maize, 
and  finds  that  it  is  inherited  as  a  simple  recessive  in 
crosses  with  the  normal  tall. 

Ateliosis*  in  man  appears  to  correspond  to  many 
of  the  ordinary  dwarf  varieties  of  plants  and  animals, 
though  Davenport  thinks  it  is  due  to  dominant  in- 
hibiting factors.  In  some  plants  at  least  smaller  cell 
size  is  involved.  A  w^ell-known  pedigree  of  the  ate- 
liotic type  of  dwarfism  occurs  in  two  families  in  the 
Tyrol  which  have  intermarried,  and  Pearson  suggests 
that  it  may  here  be  inherited  as  a  recessive  from  an 
ancestral  stock. 

Dwarfing  of  the  t^'pe  which  produces  general 
reduction  in  size  is  often  the  result  of  unfavourable 

*  Among  horses,  most  ponies,  such  as  the  Shetland  variety, 
appear  to  be  atehotic  miniatures,  while  the  Chinese  pony,  with 
short  legs  and  stout  body,  is  apparently  an  achondroplasic  dwarf. 


36  HEREDITY  AND  EUGENICS 

conditions  or  general  inhibition  to  growth.  The 
Japanese  method  of  producing  dwarf  trees  b}-  star- 
vation is  sometimes  copied  by  nature.  When  a 
tree  seedhng  germinates  in  a  cleft  of  a  rock  where 
little  nourishment  is  obtainable  it  may  struggle  on 
for  decades,  making  an  infinitesimal  amount  of 
growth  each  ^xar.  Various  instances  are  known  in 
which  domesticated  animals  in  becoming  feral  under 
a  rigorous  climate  have  decreased  conspicuously  in 
size.  This  is  probably  the  history  of  the  Shetland 
ponies  and  others.  It  is  certainly  the  origin  of  the 
somewhat  larger  ponies  from  Sable  Island,  Nova 
Scotia.  These  are  known  to  be  descended  (St.  John, 
1 921)  from  horses  taken  to  this  desolate  little  island 
from  Massachusetts.  The  historv  of  these  horses 
and  other  feral  animals  on  Sable  Island  is  of  such 
interest,  in  showing  how  a  group  of  animals  may 
react  when  removed  from  the  care  and  selection  of 
civilised  man,  that  I  refer  to  the  subject  at  some 
length.  The  facts  are  taken  from  St.  John  (1921) 
and  Gilpin  (1864). 

Sable  Island  is  a  long  crescent  of  sand  dunes,  now 
twxnt}'  miles  long  and  less  than  a  mile  wide,  about 
150  miles  east  of  Halifax,  Nova  Scotia.  When  first 
visited  in  the  sixteenth  centur}^,  it  was  apparently 
ten  miles  longer  and  two  miles  wide.  Ever}^  few 
years  a  great  storm  washes  away  some  part  of  the 
island.  The  higher  dunes  now  reach  nearly  100  feet, 
but  were  formerly  higher.  It  is  surrounded  by  shoals, 
and  hundreds  of  wrecks  have  occurred  on  its  shores, 
giving  it  the  lugubrious  distinction  of  being  the 
"  graveyard  of  the  Atlantic."  On  this  inhospitable 
island  the  Portuguese  landed  cattle  and  pigs  about 
1520.  In  1633  a  writer  reported,  "  about  800  cattle, 
small  and  great,  all  red,  and  the  largest  he  ever  saw." 
Large  numbers  of  wild  cattle  were  afterwards  shipped 
from  the  island,  according  to  a  letter  written  in  1686, 


PHYSICAL  CHARACTERS  IN  MAN         37 

and  in  i  738  there  were  no  cattle  left  there.  Evidently 
the  cattle  never  became  so  truly  feral  as  the  horses, 
which  were  landed  afterwards.  Unlike  the  latter, 
they  sought  shelter  from  human  habitations  in  storms, 
also  they  increased  in  size  and  remained  uniform  in 
colour.  The  hogs  also  ran  wild,  and  became  quite 
fierce.  But  they  w^ere  all  destroyed  in  1814  "  because 
of  their  ghoulish  tastes  when  shipwrecks  occurred." 
English  rabbits,  as  well  as  rats,  cats,  dogs,  and  foxes, 
were  introduced  in  turn,  the  native  red  and  black 
foxes  having  become  extinct.  These  introductions 
furnish  an  instructive  instance  of  how  one  species 
may  prey  upon  and  quickly  exterminate  another. 

But  the  history  of  the  horses  is  of  greatest  interest . 
In  1753  there  were  twenty  or  thirty  horses  on  the 
island  descended  from  animals  landed  some  time 
earlier.  About  1760  Thomas  Hancock,  a  Boston 
(Mass.)  merchant,  landed  horses,  cows,  sheep,  goats, 
and  pigs.  By  the  end  of  the  American  Revolution, 
all  had  been  killed  except  a  number  of  horses.  Many 
of  the  horses,  as  well  as  other  animals,  had  been  eaten 
as  food  by  shipwrecked  mariners.  The  horses  de- 
scended from  this  stock  are  well  described  by  Gilpin 
(1864),  who  visited  the  island  about  1864,  and  found 
some  400  wild  ponies  in  about  six  herds,  each  headed 
by  an  old  male  with  masses  of  mane  and  tail.  Each 
herd  had  its  own  feeding  ground,  and  they  separated 
again  when  driven  together  promiscuously.  The 
males  often  fought  savagely,  and  they  appeared  to 
sleep  standing  and  never  to  lie  down  to  rest,  alwa^^s 
fleeing  from  man  and  shelter.  Thus  in  one  hundred 
and  fifty  years  or  less  they  had  returned  to  the  habits 
of  the  wild  tarpany  horse,  with  which  they  agreed  in 
size,  hairy  heads,  and  thick  coat,  though  differing  in 
form  in  some  respects.  They  are  said  to  reproduce 
wonderfully  the  forms  of  horses  known  only  from 
the  sculptures  of  Nineveh  and  the  friezes  of  the  Par- 


58  HEREDITY  AND  EUGENICS 

thenon,  having  the  same  short  cock-thrappled  neck, 
hairy  jowl,  and  horizontal  head.  As  regards  colour, 
bays  and  browns  were  most  numerous,  then  chest- 
nuts, a  few  blacks,  no  greys,  one  probable  red  roan, 
one  pure  white,  many  piebald,  and  many  '*  bluish 
mouse  colour  "*  often  wdth  a  black  stripe  along 
the  back,  but  none  with  black  lines  around  the 
legs. 

The  striking  features  in  the  history  of  these  horses 
appear  to  be  ( i )  the  complete  reversion  to  an  ancestral 
condition,  with  change  of  form  and  decrease  in  size; 
(2)  the  large  number  of  colour  varieties.  Mere  in- 
breeding will  not  account  for  the  former.  The  colour 
varieties  may,  perhaps,  all  have  been  represented  in 
the  germ  plasm,  the  piebald  and  bluish  colours  being 
extremelv  old.  Piebald  horses  have  existed  in  all 
ages.  According  to  Gilpin,  the}^  are  depicted  on  the 
most  ancient  coins  of  China  and  w^ere  contemporary 
with  the  siege  of  Tro\^,  being  still  seen  feral  in  Northern 
Italy.  They  have  also  appeared  in  Patagonia  and 
among  the  horses  of  the  North  American  Indians. 
The  structural  changes  involved  in  the  reversion  of 
these  Sable  Island  ponies  must  have  resulted  in  some 
w^ay  from  the  rigorous  conditions.  How  the  environ- 
ment acts  in  such  cases  is  not  clear.  It  ma}^  be  parth' 
by  direct  inhibition  of  development,  and  partly  by 
selection  of  smaller  varieties  requiring  less  food.  It 
may  also  involve  the  reappearance  as  fresh  mutations 
of  conditions  which  had  previously  been  selected  out 
of  the  germ  plasm  by  the  action  of  man.  The  small 
human  races  in  some  inhospitable  climates  may, 
perhaps,  be  accounted  for  in  a  similar  wa}^ — i.e.,  by 
the  selection  of  variations,  sometimes  negative,  which 
made  survival  more  likely,  as  well  as  by  the  direct 
inhibiting    effects    of   unfavourable    conditions.     But 

*  This  "  Phrygian  cerulean  blue  of  Homer  "  is  scarcely  known 
among  modern  domestic  breeds. 


PHYSICAL  CHARACTERS  IN  MAN         39 

this  is  obviousl}^  not  the  place  to  analyse  such  possi- 
bilities from  the  evolutionary  point  of  view. 

That  the  diminution  in  size  of  a  species  may  happen 
very  quickly  is  shown  by  garden  vegetables  which 
are  allowed  to  run  wild,  or  bv  the  immediate  and 
rapid  increase  in  size  of  wild  species  taken  into  a 
garden.  This  appears  to  be  due  to  the  fact  that  con- 
ditions of  culture  permit  of  the  rapid  accumulation 
of  reserve  material.  Such  instances  as  the  following 
in  animals  show  rapid  decrease  in  size:  Dr.  John  D. 
Caton  (1887)  tells  how  a  male  and  four  female  wild 
turkeys  were  sent  from  his  grounds  in  Ottawa  to 
Santa  Cruz  Island,  twenty  miles  off  the  coast  of 
California.  This  island  is  thirt}^  miles  long  and  five 
to  ten  miles  wide.  Here  the  turke^^s  had  no  enemies 
except  a  small  grey  fox.  In  a  few  years  they  became 
ver}^  abundant  and  very  much  smaller,  the  largest 
weighing  not  over  6  pounds,  or  less  than  one-third 
the  size  of  the  first  and  second  generations  bred  there. 
In  this  case  the  mild  climatic  conditions  could  not 
have  been  responsible,  the  food  supply  was  abundant, 
the  birds  were  vigorous  and  healthy,  and  there  was 
no  evidence  of  any  epidemic.  The  wild  turkey  was 
formerly  abundant  in  Arizona,  and  birds  introduced 
on  the  mainland  of  California  north  of  San  Francisco 
were  prolific  and  of  normal  size.  The  cause  of  the 
decrease  in  size  of  the  Santa  Cruz  birds,  therefore^ 
remains  unexplained. 

Davenport  is  inclined  to  conclude  from  his  studies 
of  human  stature  that  "  in  both  ateliosis  and  achon- 
droplasia in  man  there  are  multiple  dominant  (growth 
inhibiting)  factors,  whose  actions  are  often  obscured 
by  opposing  epigenetic  growth  factors,  and  which 
are  probably  of  a  different  sort  in  ateliosis  than  in 
achondroplasia,  for  achondroplasia  affects  chiefly 
or  exclusively  the  appendages."  Evidently  much 
has  yet   to   be   learned    of   the    inheritance  of   these 


40  HEREDITY  AND  EUGENICS 

conditions  in  man,  as  well  as  concerning  the  effec- 
tive environmental  factors  which  are  involved  in 
producing  racial  differences  in  stature. 

A  condition  which  bears  some  resemblances  to 
achondroplasia,  but  was  probably  of  a  different 
character,  appeared  in  a  flock  of  sheep  in  i  791  (Hum- 
phreys, 1 813).  The  so-called  Ancon  sheep  originated 
from  a  single  ram  in  the  flock  of  a  farmer  in  Massa- 
chusetts, near  Boston.  This  ram  had  short,  bandy 
legs  and  a  short  back.  The  character  was  evidently 
a  simple  Mendelian  recessive,  and  had  probably  been 
carried  in  the  stock  for  some  time  before  it  was  brought 
out  b}'  inbreeding.  The  breed  seems  to  have  attained 
some  popularity  because  they  could  not  jump  fences ; 
but  their  crooked  forelegs,  loose  joints,  and  flabby 
subscapular  muscles  made  them  difficult  to  drive  to 
market,  their  carcasses  were  smaller,  and  they  became 
extinct  some  time  after  181 3.  This  is  an  excellent 
example  of  man's  power  over  variations  in  domestic 
animals,  first  to  multiply  them  and  afterwards  to 
bring  about  their  extinction  when  the}^  were  found 
less  serviceable. 

A  somewhat  different  account  of  the  origin  of  this 
breed  was  given  b}^  Timothy  Dwight  (1822,  vol.  iii., 
p.  134).  Hesays  that  about  i  798,  in  Mendon  township 
(Mass.),  about  eighteen  miles  south-east  of  Worcester, 
*'  an  ewe  belonging  to  one  of  the  farmers  had  twins, 
which  he  observed  to  differ  in  their  structure  from  any 
other  sheep  in  this  part  of  the  countr}^."  The  twins 
are  said  to  have  been  of  different  sex,  and  to  have  been 
bred  together  to  produce  the  new  race.  Dwight  stated 
that  their  bodies  were  thicker  and  more  clumsy, 
they  were  more  gentle,  and  have  since  multiplied  to 
many  thousands;  when  crossed  with  other  breeds, 
they  always  resembled  entirely  either  the  sire  or  the 
dam. 

The  dachshund   among  dogs   appears  to  have  re- 


PHYSICAL  CHARACTERS  IN  MAN         41 

suited  from  a  similar  mutation,  although  here  the  back 
is  long,  as  also  in  the  turnspit.  A  variety  like  the 
turnspit,  having  crooked  legs  and  a  long  back,  was 
formerly  known  among  the  pariah  dogs  of  India. 

To  quote  some  of  the  further  conclusions  of  Daven- 
port regarding  heredity  of  stature  in  man,  he  finds 
that  the  time  of  onset  of  puberty  is  probabh'  an  ele- 
ment in  determining  the  stature  ultimately  reached 
by  the  individual,  and  that  the  factors  for  tallness 
are  mostly  recessive — probabl}^  due  to  the  absence 
of  inhibitions  to  prolonged  growth.  The  least  vari- 
able offspring  are,  therefore,  the  children  of  two  tall 
parents,  all  being  usuall}^  tall,  while  tall  mated  with 
short  will  give  the  most  variable  result  owing  to  the 
recessive  factors  for  greater  stature  carried  b}^  the 
short  parent. 

An  interesting  experimental  result  bearing  on  the 
subject  of  gigantism  has  recentty  been  obtained 
by  Uhlenhuth  (192 1).  He  fed  young  salamanders 
{Ambly stoma)  on  a  pure  diet  of  the  anterior  lobe  of 
the  M'pophysis  (pituitary*)  of  cattle,  control  animals 
being  fed  with  earthworms.  A  greath'  increased 
rate  of  growth  resulted,  and  when  the  normal  adult 
size  was  reached  growth  continued  at  a  decreasing 
rate,  until  animals  of  gigantic  size  w^ere  produced. 
The  hormonef  from  the  anterior  lobe  of  the  hypophysis 
not  onl}^  accelerates  growth,  but  also  maintains 
growth  after  the  normal  adult  size  is  reached.  Carrel 
finds  that  in  tissue  cultures  the  growth  of  the  cells 
of  warm-blooded  animals  is  not  accelerated  by  hypo- 
physis extract,  and  various  investigators  have  shown 

*  The  pituitary  is  a  small  reddish  ellipsoid  organ  in  a  depression 
(the  sella  turcica)  at  the  base  of  the  skull.  It  consists  of  anterior 
and  posterior  lobes. 

t  A  hormone  is  a  chemical  substance  produced  as  an  internal 
secretion  in  a  gland  or  organ  and  carried  in  the  blood-stream  in 
minute  quantities  to  control  the  activity  of  another  organ. 


42  HEREDITY  AND  EUGENICS 

that  the  division  rate  of  protozoa  is  not  affected 
by  the  extract.  The  continued  growth  of  the  sala- 
mander is  evidently  due  to  continued  cell  multipli- 
cation rather  than  increase  in  the  size  of  cells,  the 
hormone  effect  being  probably  not  directly  on  the  cells 
of  the  body,  but  through  the  intermediary^  of  some 
other  substance  which  stimulates  cell  growth  and 
division  in  all  the  tissues. 

In  plants  it  has  been  shown  by  Bottomley  (191 7) 
that  auximones  or  growth-promoting  substances, 
bearing  certain  resemblances  to  the  vitamins,*  may 
be  obtained  from  the  water  extract  of  bacterised 
peat.  These  substances  are  probably  organic  de- 
composition products  obtained  in  peat  which  has 
partially  decomposed  under  anaerobic  conditions, 
and  is  then  acted  upon  by  aerobic  bacteria.  When 
368  parts  per  million  of  organic  matter  from  the 
water  extract  was  added  to  a  culture  of  Lemna  minor, 
grown  in  nutrient  solution,  the  effect  was  remarkable. 
In  six  weeks  the  increase  compared  with  that  of  con- 
trol plants  was  sixt^^-two  times  in  weight  and  twenty 
times  in  number  of  plants.  The  increase  in  size  was 
striking,  not  onty  as  regards  the  individual  plants, 
but  also  in  the  cells,  nuclei,  and  chloroplasts. 

That  gigantism  of  body  and  of  cells  in  plants  is 
also  often  associated  with  tetraploidy  or  doubling  in 
the  chromosome  number  has  been  shown  by  Gates 
(1909)  and  by  Tupper  and  Bartlett  (191 6),  with  de- 
tailed measurements  of  cells  and  nuclei  in  various 
tissues.  This  is  another  example  of  the  same  mor- 
phological difference  being  produced  by  an  external 
stimulus,  in  which  case  it  is  not  inherited,  or  by  a 
germinal  change,  when  it  is  inherited. 

*  Vitamins  are  substances  of  vegetable  origin  whose  presence 
in  minute  quantities  is  necessary  for  the  proper  development  of 
the  higher  animals  and  man.  In  their  absence  such  diseases  as 
scurvy,  beri-beri,  and  rickets  develop. 


PHYSICAL  CHARACTERS  IN  MAX  43 

The  data  of  inheritance  of  gigantism  in  man  include 
some  interesting  cases  in  the  tall  Scotch  population 
of  North  Carolina  and  Kentucky.  It  is  concluded 
by  Davenport  that  excessively  tall  stature  is  the 
result  of  inherited  excessive  activity  in  the  pituitary 
gland,  the  factors  for  tallness  being  mostly  recessive, 
due  to  absence  of  inhibition  to  prolonged  growth. 
It  is  clear  that  gigantism  and  dwarfism  are  not  merety 
the  extreme  terms  in  a  single  series,  but  they  are 
conditioned  in  inheritance  by  entirely  different 
ph3^siological  and  developmental  processes. 

Windle  (1891)  quotes  from  Francesco  Leporata 
the  case  of  a  dwarf  born  of  normal  parents.  At  the 
age  of  83  years  he  was  i  -i  30  metres  high.  By  a  normal 
wife  he  had  six  children  whose  heights  are  given. 
They  w^ere  all  dwarfs  but  one  normal  daughter,  their 
heights  ranging  around  that  of  the  father.  One  son, 
Antonio,  married  twice,  both  wives  being  normal, 
By  the  first  he  had  a  normal  daughter,  and  b}'  the 
second  three  children  who  were  below  normal. 
Another  son,  Pietro,  married  a  normal  woman  and 
had  three  small  children,  all  of  whom  when  measured 
were  below  the  normal  height  for  their  age.  Dwarfing 
in  this  family  appears  to  be  strongly  dominant. 

Stature  is,  of  course,  also  a  racial  characteristic. 
The  tall  races  are  found  in  North-Western  Europe, 
the  Polynesians,  North  American  Indians,  and  some 
negro  tribes  of  the  Soudan  and  Central  Africa.  Their 
height  is  68  inches  or  over.  The  short  races  comprise 
those  of  Indo-China,  Japan,  Malaya,  the  Hottentots, 
and  Eskimos.  Many  dwarfs  are  small  because  they 
cease  growth  at  an  early  age;  others  are  ver}-  small 
at  birth  and  grow  slowly.  According  to  Davenport 
(191  7),  the  average  stature  of  man  ranges  from  4  feet 
6  inches' in  the  Negrillo  Akkas  to  5  feet  10  inches  in 
the  Scots  of  Galloway.  Frederick  Wilhelm  of  Prussia 
contemplated  breeding  a  race  of  tall  grenadiers  for 


44  HEREDITY  AND  EUGENICS 

his  battalions,  and  Catherine  de  Medici  is  said  to 
have  endeavoured  to  produce  a  race  of  dwarfs  by 
bringing  about  matings  between  them. 

Eye  Colour. 

The  Mendelian  studies  of  eye  colour  up  to  191 2 
were  summarised  by  Hurst  (191 2).  He  defined  three 
patterns  of  distribution  in  the  pigmented  e^^e :  self, 
where  the  brown  is  distributed  all  the  way  to  the 
periphery  of  the  iris;  ringed,  in  w^hich  the  brown  is 
confined  to  a  ring  around  the  iris;  and  spotted,  in 
which  irregular  spots  and  patches  occur  on  a  blue 
background.  The  blue  or  grey  colour  represents 
absence  of  brown  pigment,  and  is  simply  the  apparent 
colour  of  the  muscle  fibres  in  the  iris  as  seen  through 
the  cornea. 

A  recent  paper  (Boas,  1919)  presents  statistics 
of  e3'e  colour  which,  it  is  claimed,  do  not  support  the 
Mendelian  contention  that  two  blue-eyed  individuals 
have  only  blue-eyed  offspring.  But  the  wTiter  admits 
that  in  collecting  these  data,  persons  with  a  certain 
amount  of  brown  in  their  eyes  may  have  been  classed 
as  blue-e^^ed.  Pearson  and  others  have  also  studied 
carefully  some  of  the  more  detailed  differences  in  eye 
pigmentation  which  are  important  for  a  complete 
anah^sis.  It  is  clear  that  the  conception  of  a  single 
Mendelian  factor  difference  between  brown  and  blue 
e\^es  is  only  a  rough  first  approximation  in  the  study 
of  this  subject. 

Usher  (1920),  from  a  careful  histological  examina- 
tion of  six  albino  eyeballs,  found  traces  of  pigment  in 
four.  The  fifth  was  unknown,  and  the  sixth,  that  of  an 
infant,  was  devoid  of  pigment.  Usher  therefore  con- 
cludes that  total  absence  of  pigment  cannot  be  used 
as  a  definition  of  albinism  in  man .     The  fovea  centralis* 

*  This  is  a  pit  in  the  middle  of  the  macula  lutea  or  point  of 
clearest  vision  at  the  centre  of  the  retina. 


PHYSICAL  CHARACTERS  IN  MAN         45 

in  albinotic  eyes  is  shown  to  be  absent  or  imperfect, 
and  this  may  be  the  chief  cause  of  the  imperfect  vision 
in  such  eyes.  In  the  eyes  of  albinotic  individuals 
belonging  to  dark  races  the  mesoblastic  pigment 
appears  earlier  and  is  found  in  much  larger  quantity 
at  time  of  birth  than  in  European  eyes.  Chemical 
examination  indicates  that  there  is  more  pigment  in 
the  eyes  of  albinos  of  dark  races  than  of  white  races. 
This  is  in  line  with  much  evidence  from  mammals 
of  a  close  relation  between  density  of  coat  colour  and 
of  eye  pigmentation. 

Recent  studies  of  brown  and  blue  eyes  indicate 
that  they  are  not  alw^ays  a  simple  pair  of  Mendelian 
characters  as  formerly  supposed,  but  sex-linkage 
and  other  complications  may  come  in.  Br^^n  (1920) 
collected  statistics  in  Norw^ay  and  states  that  in  four 
out  of  thirty  marriages  tw^o  blue-eyed  parents  had 
some  brown-eyed  children.  From  these  four  mar- 
riages there  were  ten  children  with  brow^n  eyes  and 
seventeen  with  blue.  One  or  both  grandparents,  in 
all  cases,  had  brown  eyes.  Winge  (1921),  in  a  much 
more  extended  studv,  criticises  these  results  and 
concludes  that  such  cases  are  exceedingly  rare  if  the 
parents  have  normal  vision.  By  means  of  a  question- 
naire, Winge  collected  data  of  eye  colour  in  about 
1 ,400  children  of  natural  history  association  members 
in  Denmark  and  their  parents.  The  data  obtained 
were  carefully  sifted,  and  the  results  are  given  in  the 
table  on  p.  46. 

From  the  table  it  will  be  seen  that,  in  addition  to 
the  seven  children  with  doubtfull}^  blue  eyes  from 
blue-eyed  parents,  twelve  children  (belonging  to  eight 
families)  had  brown  pigment  in  their  eyes.  Further 
information  obtained  from  five  of  the  families  indi- 
cates that  the  condition  was  due  in  two  cases  to 
abnormalities  in  the  eye.  In  another  family  of  seven, 
two  of  the   daughters  had  some  brown  pigment  in 


46 


HEREDITY  AND  EUGENICS 


their  eyes,  and  one  of  the  latter  married  a  blue-eyed 
man  and  had  six  children,  all  blue-e3^ed.  This  case 
is  thought  to  be  explained  b}"  assuming  that  one  of  the 
grandparents  was  genot3'picalh^*  brown-eyed  but  had 
a  "  pigment  restrictive  disposition  "  which  made  him 
or  her  phenotypically  (that  is,  visibty)  blue-eyed. 
The  brown-eyed  daughter  having  blue-eyed  children 
is  explained  by  sex-linked  inheritance.  It  is  shown 
from  other  evidence  that  pigment-inhibiting  factors 
ma}"  be  accompanied  by  abnormalities  in  vision, 
but  the  interpretations  in  this  part  of  the  paper  are 
not  always  convincing. 

TABLE  I. 
Inheritance  of  Eye  Colour  (Winge). 


Number 

of 

Children. 

Marriages. 

Blue. 

1 

Browfi 

I. 

Greyish-Green 

or 
Bluish-Green. 

Total. 

Blue  X  blue 
Blue  X  brown  and 

conversely 
Brown  x  brown 

625 

'317 
25 

12 

322 
82 

7 
9 

i 

644 

648 
107 

Total 

967      i 

416 

1 

16 

1,399 

Perhaps  the  most  interesting  results  of  Winge 
concern  the  sex-linked  inheritance  of  eye  colour. 
The  statement  that  there  are  more  brown-eyed 
women  than  men  was  borne  out  by  statistics  of 
300,000  school  children,  collected  by  S.  Hansen. 
Similar  results  have  been  obtained  by  others.  Winge 
shows  the  fact  of  sex-linkage  by  giving  the  results 
of  marriages  in  which  the  parents  had  different  e^^e 
colour.     These  are  appended  in  the  following  tables  : 

*  That  is,  in  inherited  germinal  constitution. 


PHYSICAL  CHARACTERS  IX  MAN 


47 


TABLE  II. 
Mother  Blue  x  Father  Browx. 


Eye  Colour  of  Children. 

Sons. 

Daughters. 

Total. 

Blue 

Brown    .  . 

Greyish-green  or  bluish-green 

63 

65 

4 

50 

81 

2 

113 

146 

6 

Total 

132 

133 

265 

TABLE  III. 
Mother  Brown  x  Father 

Blue. 

Eye  Colour  of  Children. 

Sons. 

Daughters. 

Total. 

Blue 

Brown    .  . 

Greyish-green  or  bluish-green 

lOI 

87 

■        103 

89 

3 

204 
176 

3 

Total 

188 

195 

383 

Clearly  from  the  tables,  when  the  father  has  brown 
eyes,  half  the  sons  have  blue  e3"es  and  half  brown, 
but  many  more  daughters  have  brown  than  blue 
eyes,  although  the  total  numbers  of  the  sexes  are 
equal.  On  the  other  hand,  when  the  mother  has 
brown  eyes  there  is  a  marked  excess  of  blue-eyed  sons 
and  daughters.  After  an  elaborate  analysis  these 
results  are  explained  by  assuming  that  in  addition 
to  the  simple  pair  of  factors  originally  recognised, 
there  is  another  dominant  factor  for  brown  eyes 
which  is  sex-linked  in  inheritance.  The  writer  is 
further  obliged  to  assume  that  female  germ  cells 
(b  W)  containing  the  sex-linked  factor  (W)  together 
with  the  ordinary  determiner  for  blue,  cannot  exist. 
It  should  not  be  difficult  to  obtain  extensive  data  of 
eye  colour  to  test  these  h3'potheses.  All  the  assump- 
tions  made   are   reasonable   enough   in   the   light    of 


48  HEREDITY  AND  EUGENICS 

present  genetic  knowledge.  It  is  well  known  that 
in  rabbits  and  guinea-pigs  factors  for  coat  colour  also 
often  affect  e^^e  colour. 

Having  stated  some  of  the  facts  as  found,  several 
criticisms  of  the  present  Mendelian  position  as  regards 
e3^e  colour  are  necessary.  In  the  first  place,  many 
grades  of  brown  exist,  both  as  regards  shade  of 
colour  of  the  iris  and  distribution  of  pigment.  In  an 
accurate  study  of  eye  colour  these  shades  and  varying 
distributions  should  be  distinguished,  and  only  lumped 
together  for  certain  statistical  purposes.  It  may 
turn  out  that  all  the  shades  of  iris  pigmentation  do 
segregate  sharpty  from  pure  blue,  but  much  more 
extensive  and  accurate  data  will  be  required  than  are 
at  present  available  before  any  certain  conclusions 
can  be  drawn.  It  appears  that  even  a  difference 
in  pigmentation  of  the  two  eyes  ma}^  be  inherited  in 
certain  families,  and  when  the  effects  of  various 
abnormalities  of  the  eye  in  distorting  or  inhibiting 
the  pigmentation  of  the  iris  are  considered,  the  neces- 
sity for  accurate  and  prolonged  observation  is  obvious. 
On  the  other  hand,  in  the  light  of  the  complications 
as  regards  eye  pigmentation  disclosed  in  Drosophila, 
it  is  by  no  means  improbable  that  w^hen  sufficiently 
anah'sed,  the  pigmentation  of  the  iris  in  man  will  be 
found  also  to  follow^  Mendelian  laws.  But  it  is  neces- 
sary to  emphasise  the  necessity  of  very  accurate 
and  detailed  first-hand  observations  of  parents  and 
children.  The  existence  of  all  intergrades  of  colour 
and  distribution  of  pigment  in  the  iris  is  well  known. 
Whether  the  detailed  facts  will  bear  a  complicated 
Mendelian  analysis  remains  to  be  seen,  but  there  is 
nothing  at  present  to  negative  that  possibilit}^. 

The  writer  recently  had  the  opportunit}'^  of  ex- 
amining the  e3^e  colour  of  people  in  Bergen,  Norway. 
Only  about  one  in  fifteen  would  be  roughly  classed 
as    brown-eyed,    but    the    blues    varied    continuously 


PHYSICAL  CHARACTERS  IN  MAN  49 

from  very  light  to  very  dark  blue,  and  so  through 
greenish  or  yellowish  shades  (due  to  a  small  amount 
of  brown  pigment)  to  pale  brown,  dark  brown  being 
rare.  Every  grade  of  colour  appeared  to  be  repre- 
sented, with  a  great  predominance  of  the  paler  shades. 

Sedgwick  (1861)  describes  an  interesting  family  in 
County  Wexford,  Ireland,  with  tortoiseshell-coloured 
eyes.  The  third  generation,  numbering  sixteen  sons 
and  five  daughters,  all  had  the  peculiarity,  which  they 
inherited  from  their  mother.  The  mother  had  three 
sisters  and  a  brother  with  the  same  colour  of  eyes, 
which  was  in  turn  inherited  from  their  mother.  Hence 
the  character  was  a  simple  Mendelian  dominant. 

Bond  (191 2)  has  studied  the  inheritance  of  the  con- 

•  ^    D 

i   4  4  4  4xD 


I  I 

/6  Sons  5  Dau. 

Fig.    9. ^TORTOISESHELL-COLOURED    EyES. 


dition  known  as  heterochromidia  iridis,  in  which  the 
two  eyes  are  of  different  colour.  In  addition  to  the 
patterns  recognised  by  Hurst,  he  distinguishes  between 
self  colour  and  the  ray  pattern,  in  which  only  one  or 
more  sections  of  the  iris  are  pigmented.  This  con- 
dition is  a  fairly  frequent  one,  and  shows  inheritance, 
though  the  position  of  the  ra}^  or  sector  is  variable 
from  one  generation  to  another.  Bond  finds  that  the 
two  eyes  are  unlike  in  pigmentation  in  perhaps  one  or 
two  individuals  per  1,000.  In  rabbits  the  condition  is 
much  more  common,  sometimes  four  in  100.  Horses 
with  a  ''  wall  "  eye  are,  of  course,  well  known,  and  in 
various  breeds  of  dogs,  such  as  Great  Danes,  English 
collies,  and  Old  English  sheep  dogs,  the  condition  is 
not  uncommon.       In  both  horses  and  dogs  it  is  fre- 

4 


50  HEREDITY  AND  EUGENICS 

quently  associated  with  a  patchy  or  piebald  coat. 
Both  conditions  nia}^  arise  when  self  colour  is  raated 
with  w^hite,  and  in  some  cases  it  may  be  looked  upon 
as  a  phenomenon  of  disintegration  following  on  the 
quantitative  dilution  of  a  factor  for  pigmentation. 
It  resembles  in  this  respect  the  striping  of  flowers 
(see  p.  58).  Because  factors  may  be  diluted  and 
disintegrated  in  this  w^ay  by  crossing,  it  is  not  neces- 
sar}'  to  assume,  as  Bond  does,  that  there  were  originally 
independent  factors  for  each  eye  and  subordinate 
factors  independently  controlling  different  areas  of 
the  iris.  There  is  no  evidence  that  factors  have  been 
built  up  in  this  way.  They  appear  rather  to  originate 
as  germinal  changes  or  new  conditions  of  equilibrium, 
which  may  later  become  modified  by  crossing  or 
otherwise. 

A  number  of  observations  on  the  e^^e  colours  of 
birds  and  their  inheritance  are  recorded  b}^  the  same 
writer  (Bond,  191 9).  His  studies  were  chiefly  of 
pigeons  and  fowls,  although  references  are  made  to 
many  other  species.  The  pigment  granules  producing 
eye  colour  may  be  black,  brown,  ^^ellow,  ruby,  or 
pearl.  The  ''  bull  "  eye  owes  its  black  colour,  as 
in  the  white  fantail  pigeons,  to  the  absence  of  pig- 
ment from  the  anterior  surface  of  the  iris.  The  pos- 
terior uveal  pigment  shines  through  the  translucent 
tissues  of  the  iris  and  gives  the  eye  its  colour,  as  in 
blue  human  eyes.  Also,  as  with  blue  eyes  in  man,  the 
"bull"  eye  of  the  chick  is  retained  in  the  adult. 
The  ruddy  glow  of  this  e3"e  is  due  to  the  plexus 
of  bloodvessels.  (A  similar  t3^pe  of  eye  occurs  in 
guinea-pigs  of  the  type  which  Castle  calls  red-eyed 
silver  agouti).  But  in  most  birds  with  dark  or  black 
eyes,  the  colour  is  due  to  the  presence  of  anterior 
iris  pigment.  In  the  rock  pigeon  {Columba  livia)  the 
iris  colour  is  yellow  or  orange,  while  in  other  pigeons 
it  may  be  white  or  red,  and  in  the  stock  dove  (C.  cenas) 


PHYSICAL  CHARACTERS  IN  MAN  51 

the  e\^e  is  peculiar,  its  black  colour  being  due  to  the 
presence  in  the  iris  and  in  deeper  tissues  of  branching 
cells  packed  with  dark  granules. 

In  the  pearl  or  white  eye  of  pigeons  and  the  "  daw  " 
eye,  as  in  the  Malay  fowl,  there  is  no  anterior  pigment 
in  the  iris,  but  its  tissues  are  opaque,  owing  to  the 
presence  of  crow^ded  colourless  granules.  This  ap- 
parently corresponds  with  the  "  wall  "  eye  in  horses, 
dogs,  and  pigs.  The  muscle  fibres  of  the  avian  e3^e, 
however,  are  striated  or  voluntary,  and  not  plain  as 
in  the  mammals.  Pearl  eye  in  pigeons  is  recessive 
to  yellow  or  "  gravel  "  eye,  as  "  daw  "  e^^e  in  fowls 
is  to  amber  or  black  eye  when  the  latter  is  due  to 
anterior  pigment.  The  yellow  eye  derives  its  colour 
from  a  network  of  branching  cells  containing  yellow 
granules.  If  the  latter  are  closely  packed,  the  eye 
may  appear  black.  In  fowls  the  ^^ellow  e3^e  ma}'  be 
due  to  (i)  granules  in  the  connective  tissue  cells; 
(2)  granules  in  the  striated  muscle  cells,  as  in  Dorkings 
and  Orpingtons.  In  owls  the  yellow  eye  is  due  to 
bright  3"ellow  granules  in  cells  coating  the  iris. 

Brown  and  black  eyes  in  birds  are  produced  b}'  a 
layer  of  branching  cells  on  the  iris  containing  dark 
pigment  granules.  Ruby  e3^es  are  produced  in  various 
ways  in  different  birds  ;  and  some  birds,  such  as  certain 
birds  of  paradise,  have  parti-coloured  irides.  Gene- 
tically, black  due  to  pigmented  iris  is  dominant  over 
yellow  and  other  grades  of  iris  pigmentation. 

Skin  Colour  and  Hair  Characters. 

Hurst  (191 2)  has  summarised  the  studies  on  hair 
and  skin  colour  in  man,  and  added  some  observations 
of  his  «wn.  The  main  points  with  regard  to  hair 
colour  are:  (i)  That  the  brown  shades  of  colour 
appear  to  be  continuous  from  white  (albino)  hair  to 
jet  black;  (2)  the  reds  form  a  separate  series  due  to  a 


52  HEREDITY  AND  EUGENICS 

lipochrome  (a  group  of  animal-fat  pigments),  while 
the  brown  is  a  melanin  (a  dark  pigment  found  in  hair, 
etc.);  and  (3)  the  generalisation  of  the  Davenports 
(1910)  that  (with  rare  exceptions)  children  never 
have  darker  hair  than  their  darker  parent.  This 
''  non-transgressibility  of  the  upper  limit  "  applies 
also  to  skin  colour  or  complexion  in  the  white  races. 
Davenport  (191  3),  from  a  study  of  mulatto  families 
in  Bermuda,  Jamaica,  and  the  United  States,  con- 
cluded that  there  are  probably  two  segregating 
Mendelian  factors  for  black,  and  that  other  negroid 
features,  such  as  kink}^  hair  and  thick  lips,  segregate 
independently.  The  same  would  appear  to  be  true  for 
mental  characters,  since  mulattoes  sometimes  display 
high  intellectual  ability,  but  never  pure  negroes,  as 
far  as  is  known. 

The  evidence  in  favour  of  a  strictly  Mendelian  ex- 
planation of  colour  inheritance  in  white-black  crosses 
is,  however,  by  no  means  conclusive.  Pearson  (1909), 
from  data  supplied  b}^  a  medical  man  in  the  West 
Indies,  gives  quite  a  different  picture.  The  first  cross 
gives  a  brown  mulatto  or  a  yellow  mulatto,  and  the 
basis  or  cause  of  this  difference  is  not  apparent.  In 
crosses  between  mulattoes  "  there  are  now  and  then 
slight  variations  from  the  usual  mulatto  brown  or 
mulatto  yellow,"  but  never  pure  black  or  white. 
Sports  or  throwbacks  rarely  occur,  but  the  form 
where  the  tint  is  barely  evident  is  said  to  be  not 
uncommon.  Mulatto  x  negro  produces  the  sambo, 
a  deep  mahogany  brown,  and  it  is  said  there  is  never 
any  other  colour  from  this  cross.  Mulatto  x  white 
produces  the  quadroon,  which  is  never  pure  white, 
but  almost  invariably  lighter  than  the  brown  mulatto 
and  nearly  always  lighter  than  the  yellow  mulatto. 
This  gives  the  impression  of  intermediac}^  in  the 
various  hybrid  conditions,  with  a  not  very  marked 
tendency   to   segregation,   which   is   never   complete. 


PHYSICAL  CHARACTERS  IN  MAN         53 

Evidentl}^  what  is  required  is  an  extensive  collection 
of  accurate  data  based  on  careful  measurements  of 
pigmentation  with  colour  tops  before  this  complex 
subject  can  be  fully  understood.  Probably  something 
more  complicated  than  the  two-factor  hypothesis 
of  Davenport  is  required  to  explain  all  the  facts  of 
colour  inheritance  in  white-black  crosses.  In  how 
far  real  permanent  blends  occur  remains  to  be  seen. 
Although  individuals  occur  in  later  generations  who 
pass  for  whites,  it  is  not  certain  that  the  pigment 
is  ever  entirely  lost,  though  it  is  probable  that  the 
presence  of  other  negroid  features  gives  the  impression 
that  more  black  pigment  has  been  retained  than  in 
the  normal  brunette  skin. 

Jordan  (191 1),  in  a  histological  stud}'  of  melano- 
genesis  in  mulatto  and  white  skins,  finds  that  the 
only  factor  in  skin  pigmentation  is  the  number  of 
(yellowish-brown)  granules  and  the  number  of  cells 
containing  such  granules.  Some  mulattoes  are  iden- 
tical with  negroes  and  others  with  brunettes  in  amount 
of  pigment.  The  apparent  continuit}'  in  the  melano- 
genetic  process  is  believed  to  rest  in  mulatto  families 
upon  discontinuities  or  discrete  units  controlling  the 
production  of  melanin  granules.  Such  conditions 
conform  more  or  less  closely  to  an  alternative  mode 
of  inheritance. 

Sedgwick  (1863)  refers  to  silvery  grey  hair  of  very 
coarse  texture  as  being  present  in  about  one  in  ten  or 
twelve  of  the  Mandan  Indians,  irrespective  of  age. 

The  various  types  of  hair  in  the  different  races  of 
man — straight,  wav}',  kink}',  and  curly — are  known 
to  differ  in  the  shape  of  a  cross-section,  straight  hair 
being  circular  in  cross-section,  kinky  hair  elliptical, 
with  the  other  t3'pes  intermediate.  Little  is  actually 
known  regarding  the  inheritance  of  these  differences. 
Bean  (1908)  has  studied  the  hair  types  among  the 
h3'brid  Filipinos,  in  which  the  Chinese  element  fur- 


54  HEREDITY  AND  EUGENICS 

nished  the  straight  t3^pe  of  hair.  Hair  was  classed 
as  straight  when  the  relative  diameters  in  cross- 
section  were  100:90  or  over,  wav}^  when  100:70-90, 
and  curly  when  100:60-70.  In  31  families  in  which 
the  cross  was  wavy  X  straight  or  curh'  x  straight, 
there  were  i  57  children,  of  whom  84  had  straight  hair 
to  73  curly  or  wavy.  This  approximates  to  a  Men- 
delian  i  :  i  ratio;  but  dominance,  when  it  occurs,  is 
variable,  and  although  segregation  occurs  to  some  ex- 
tent, there  is  no  close  conformit}'  to  simple  Mendelian 
behaviour.  Wav}^  is  regarded  as  a  heteroz^'gote  of 
curly  and  straight,  curh^  being  recessive,  but  there 
is  no  sharp  line  between  wavy  and  curl}'.  W^avy  x 
wavy  gives  all  three  types  in  approximately^  equal 
proportions.  Straight  X  straight  gives  all  three 
types,  but  with  a  large  preponderance  of  straight. 
Curh'  X  straight  gives  mostly  straight  if  the  father's 
hair  is  straight,  but  more  curly  if  the  father's  hair 
is  curly.  These  results  for  Filipinos  appear  to  be 
general!}'  the  reverse  of  those  obtained  in  America. 
(See  photographs  in  Journal  of  Heredity  7:412  [191 6].) 
Bond  (191 2)  cites  certain  cases  of  negro-white  crosses 
in  which  wavy  and  kinky  hair  both  appear  in  the 
same  individual,  the  hair  being  wavy  on  the  vertex 
and  kinky  on  the  sides  of  the  head.  Three  such 
cases  are  figured. 

In  a  little-known  work  on  the  hair  of  mankind, 
Friedenthal  (1908)  gives  descriptions  with  numerous 
coloured  plates  showing  the  distribution  of  hair  on 
the  human  body,  and  the  extremes  of  plus  and  minus 
variation  in  various  races  of  man  and  in  some  apes. 
Aino  of  Japan  are  figured,  in  some  of  which  almost 
the  entire  body  has  a  hairy  covering,  and  these  are 
compared  with  certain  European  variations  in  which 
the  whole  face  is  covered  with  hair.  Darwin*  cites  a 
Siamese  family  which  for  three  generations  had  the  face 

*  Animals  and  Plants,  i.  448. 


PHYSICAL  CHARACTERS  IN  MAN         55 

and  body  covered  with  long  hair.  This  was  accompa- 
nied by  deficient  teeth.  He  also  refers  to  a  woman  with 
completely  hairy  face,  exhibited  in  London  in  1663. 

E.  Fischer  (1910)  has  given  the  history  of  an 
interesting  family  in  Upper  Alsace,  near  Colmar, 
some  of  whose  members  were  almost  entirely  devoid 
of  hair.  Daniel  BoUenbach,  belonging  to  the  second 
generation  of  the  pedigree  (see  Fig.  10),  had  no  hair 
of  the  ordinary  type,  but  his  whole  head  bore  a  very 
scattered,  soft  down,  about  i  centimetre  long,  com- 
posed of  soft,  thin,  colourless  hairs.  Under  the 
microscope  they  are  seen  to  have  no  central  medulla 
or  pigment  granules,  to  be  somewhat  thinner  than 
ordinary  hair,  and  twisted.  Amongst  these  are  a  very 
few  longer  (3  centimetres)  and  somewhat  thicker, 
pale  reddish,  delicate  hairs.  Under  the  microscope 
these  show  a  normal  central  medulla  and  a  weak 
reddish-brown  pigmentation.  Eyebrows  and  e3^e- 
lashes  are  lacking.  The  arms  and  legs  are  hairless ; 
also  there  is  no  breast  hair  or  axillary  hair.  The 
nails  of  the  toes  and  fingers  are  deformed,  becoming 
thick  and  rough.  The  teeth  deca\'ed  early,  leaving 
many  stumps.  There  is  here  the  well-known  corre- 
lation between  deficiencies  in  teeth,  nails,  and  hair. 
Some  other  members  of  the  familv  have  a  few  hairs 
on  the  body  = 

The  inheritance  of  this  hairless,  condition  shows 
peculiarities  (see  chart.  Fig.  10),  which  are  difficult  to 
explain  except  perhaps  on  an  hypothesis  of  variable 
or  reversed  dominance  of  a  single  Alendelian  factor. 
The  character  itself  seems  to  have  appeared  suddenty 
through  a  germinal  change,  since  the  two  generations 
preceding  its  original  appearance  were  all  normal, 
although  they  included  cousin  marriages  which  would 
probably  have  brought  out  a  recessive  character  it 
it  had  been  present.  It  will  be  seen  (Fig.  10)  that  in 
the  Fi  Mathias,  who  was  normal,  had  only  normal 


56 


HEREDITY  AND  EUGENICS 


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PHYSICAL  CHARACTERS  IN  MAN  57 

descendants,  but  Katherine  (abnormal)  also  had  only 
normal  descendants  through  three  generations.  If 
the  character  were  recessive  its  absence  here  would 
be  explained,  since  her  husband  was  probably  homo- 
zygous normal.  Maria  and  Salome,  if  their  husbands 
(Bollenbach)  were  heterozygous,  should  have  half 
their  children  of  each  type.  The  actual  numbers  were 
three  normals  to  four  hairless  and  seven  normals  to 
seven  hairless  respectively.  The  numbers  are,  of 
course,  too  small  to  make  a  certain  interpretation, 
but  the  most  likely  interpretation  appears  to  be  that 
the  character  behaved  as  a  recessive.  In  the  case  of 
Katherine,  it  is  very  unlikely  that  it  would  fail  to 
appear  in  any  of  her  four  children  if  it  were  dominant. 
The  fact  that  the  sex  of  so  many  of  the  children 
is  unrecorded  indicates  that  the  records  are  not, 
perhaps,  very  accurate. 

Inbreeding  does  not  explain  the  origin  of  this 
character,  which  was  probably  due  to  germinal  change, 
and  if  the  Bollenbachs  were  homozve^ous  it  would 
behave  partly  as  a  dominant.  The  abnormal  section 
of  the  family  is  fast  dying  out.  Sexual  selection  is 
apparently  a  factor,  for  abnormal  members  of  the 
family  often  remain  single.  Of  the  fourteen  children 
of  Salome,  all  died  but  one  (Daniel),  who  had  two 
children,  only  one  of  which  reached  maturity.  Michel 
remained  childless.  Only  two  abnormal  members  of 
this  famil}^  remain — both  old  men.  At  their  death, 
the  abnormality  will  be  lost  after  fifteen  abnormal 
individuals  had  appeared  in  three  generations.  This 
is  a  marked  case  of  an  abnormality  appearing  sud- 
denly and  then  disappearing  in  a  few  generations. 

Albinism 
The  monograph  on  albinism  in  man,  by  Pearson, 
Nettleship,  and  Usher  (1911-1913)  is  a  very  elaborate 
and  detailed  treatment,  which  will  serve  as  a  basis 


58  HEREDITY  AND  EUGENICS 

for  all  future  studies  on  this  subject.  It  gives  not 
only  an  elaborately  illustrated  description  of  the  ex- 
ternal features  and  the  histolog}^  of  the  skin  and  e^'^e 
pigmentation  in  albinotic  individuals,  but  also  deals 
with  the  histor}^  of  the  subject.  Pure  albinism  is  a 
recessive  character* :  but  the  condition  exists  in  vary- 
ing degrees,  and  its  inheritance,  like  that  of  so  many 
human  qualities,  frequently  shows  complications. 
Complete  albinism  occurs  in  both  white  and  coloured 
races  of  man.  Pearson  divides  albinotics  into  six 
classes.  Several  cases  of  white  spotting  in  negroes, 
similar  to  the  classical  types  seen  in  paintings  of  the 
eighteenth  century,  have  been  described  in  modern 
times.  The  evidence  certainl}^,  as  Pearson  (191 3) 
contends,  favours  the  hypothesis  that  spotting  arises 
de  novo  where  a  white-black  cross  or  mixed  race  is 
crossed  back  with  a  pure  white  or  black.  In  other 
words,  spotting  ma}^  be  considered  to  arise  in  certain 
cases  as  a  somatic  segregation,  repulsion,  or  dilution 
effect,  and  not  to  be  clue  to  an  inherited  invisible 
spotting  factor.  Striping  in  various  flowers  is 
generall}^  believed  to  have  originated  in  the  same  wa}^ 
A  similar  case  occurs  in  certain  (Enothera  hybrids 
(Gates,  191  5).  When  (E.  ruhricalyx  having  dark  red 
buds  is  crossed  with  CE.  grandiflora  having  green  buds, 
the  F;^  is  paler  red.  If  this  F^  generation  is  crossed 
back  with  Qi.  grandiflora,  the  colour  is  further  diluted, 
becoming  very  pale;  and  in  some  families  the  pattern 
breaks  up  into  spots,  a  condition  which  is  inherited. 

Once  this  spotted  condition  has  arisen,  it  appears 
then  to  be  fairly  stable.  Cases  of  human  albinotic 
spotting  are  on  record  which  have  been  transmitted  for 
two  to  five  generations  (Stannus,  191 3).  The  con- 
dition of  spotting  has,  in  some  way,  become  stabilised 
in   the  germ  plasm,  and   should,  therefore,  probably 

*  A  recent  case  in  which  two  complete  albino  "  white  " 
parents  had  an  albino  son  is  illustrated  by  Davenport  (19 16). 


PHYSICAL  CHARACTERS  IN  MAN         59 

be  looked  upon  as  a  mutation  following  crossing. 
Moreover,  the  spotting  in  man  often  follows  a  charac- 
teristic pattern,  beginning  as  a  blaze  in  the  forehead, 
with  spotting  of  the  arms,  the  back  largely  black, 
as  well  as  the  extremities.  Curiously  enough,  photo- 
graphs of  the  Honduras  piebald  (Pearson,  191 3)  seem 
to  show^  an  extension  of  some  of  the  coloured  spots  as 
the  child  develops.  The  sporadic  manner  in  which 
spotting  appears  in  all  such  cases  remains  to  be  ac- 
counted for.  The  Honduras  piebald  had  five  siblings,* 
all  normal  mulattoes.  His  mother  combined  Mexican 
and  negro  blood,  W'hile  the  father  was  a  pure  negro. 

In  an  interesting  case  recorded  by  Dr.  vSt annus 
and  cited  in  the  monograph  on  albinism,  piebaldism 
was  found  to  occur  in  five  generations  of  a  family  of 
natives  at  Florence  Bay,  Nyasaland,  appearing  in 
nine  individuals.  Albinotic  patches  occurred  in 
the  median  line,  on  the  anterior  half  of  the  scalp, 
in  the  epigastric  region,  and  broad  "  garters  "  about 
the  knees.  The  inheritance  here  extended  to  the 
position  of  the  patches. 

In  an  English  family  the  inheritance  of  a  white 
forelock  has  been  traced  through  six  generations  by 
Harman  {Trans.  OphUiaf.  Soc,  1909).  The  white 
forelock  is  accompanied  by  a  patch  of  white  skin 
spreading  like  a  flare  down  the  middle  of  the  forehead. 
In  some  members  of  the  famih^  there  are  also  patches 
of  pure  w^hite  skin  on  the  median  line  of  the  trunk 
or  the  inner  sides  of  the  calves.  The  eyes  were  normal, 
with  no  white  eyelashes  or  parti-coloured  irides. 
The  members  of  the  family  are  long-lived  and  robust, 
but  have  a  tendency  to  early  w^hitening  ot  the  hair. 
This  piebald  marking  was  found  in  twenty-four 
individuals  belonging  to  nine  childships  among  a 
total  of  138  individuals  in  the  six  generations.  The 
children  of  normals  were  all  normal.  In  the  first 
*  This  term  means  brothers  and  sisters  taken  collectively. 


6o  HEREDITY  AND  EUGENICS 

three  generations  all  showing  the  mark  were  females, 
but  in  the  last  three  generations  affected  males  and 
females  were  equal  in  numbers,  and  inheritance  was 
thought  to  be  through  the  males  only.  The  data 
indicate,  however,  that  the  peculiarit}^  is  inherited 
as  a  simple  Mendelian  dominant,  chance  accounting 
for  the  absence  of  affected  males  in  the  early  genera- 
tions, and  the  small  number  of  females  who  were 
mothers  in  the  later  generations  accounting  for  the 
later  lack  of  transmission  through  the  mothers. 

Pearson  (1921)  has  recentl}^  described  another 
very  similar  case,  with  a  white  patch  or  flare  on  the 
forehead  and  hair.  In  this  famity  there  were  seven 
affected  members  hi  four  generations.  This  family 
also  goes  gre}"  ver}^  earty,  and  there  is  some  tuber- 
culosis but  no  consanguinity.  This  feature,  of  course, 
resembles  the  white  "  star  "  marking  often  seen  in 
the  forehead  of  horses  and  cattle,  and  frequentl}^ 
accompanied  by  white  patches  on  the  extremities. 
In  this  family  the  original  great-grandmother  in  the 
pedigree  must  have  been  heterozygous.  In  the 
succeeding  three  generations  the  numbers  of  members 
which  were  normal  or  flared  were  respectively  3:2, 
4:1,  and  6:3,  making  a  total  of  13:6.  This  is  a  rather 
wide  departure  from  the  ratio  which  would  be  ex- 
pected if  the  trait  were  a  simple  dominant,  the  odds 
against  its  occurrence  being  17-5  to  i.  But  since  un- 
affected members  never  transmit  the  flare,  it  cannot 
be  a  regular  recessive.  If  the  character  is,  as  in  other 
cases,  a  simple  dominant,  the  small  numbers  showing 
the  flare  might,  perhaps,  be  accounted  for  on  the 
assumption  of  the  decreased  viability  of  such  hetero- 
z3'gous  individuals. 

The  occurrence  and  inheritance  of  a  differently 
coloured,  usually  white,  patch  of  hair,  is  a  fairl}- 
common  phenomenon.  Darwin  {Animals  and  Plants 
under   Domestication,   chapter    xii.)    cites   an    English 


PHYSICAL  CHARACTERS  IN  MAN         6i 

family  in  which  "  for  maii}^  generations  some  members 
had  a  single  lock  differently  coloured  from  the  rest 
of  the  hair,"  and  an  Irish  family  in  which  a  small 
white  lock  occurred  in  son,  mother,  and  grandmother. 

Cockayne  (1914)  states  that  piebalds  are  very  un- 
commion  both  in  black  and  white  races.  He  describes 
a  piebald  English  family  of  six  generations  with  nine- 
teen affected  mem_bers,  belonging  to  a  farming  stock 
near  Bury  St.  Edmunds,  Suffolk.  Some  members 
of  the  famil}^  are  fair  and  some  dark,  but  both  inherit 
the  peculiarity,  which  consists  of  a  blaze  in  the  fore- 
head. Three  members  of  this  family  have  hetero- 
chromidia  iridis,  and  some  have  additional  white 
patches  of  skin  on  the  body.  In  the  last  four  genera- 
tions of  affected  families  the  total  num.bers  are  seven- 
teen having  the  flare  to  twelve*  normal.  This  is  near 
enough  to  the  equality  which  would  be  expected 
if  the  flare  were  a  heteroz^^gous  dominant  condition, 
and  is  in  general  accord  with  Pearson's  case,  but  the 
excess  is  on  the  other  side  and  is,  perhaps,  not  signi- 
ficant in  either  case.  We  ma}-,  then,  conclude  that 
the  flare  behaves  as  a  simple  dominant,  at  least  in 
these  three  independent  families,  and  in  the  two  de- 
scribed in  the  following  paragraphs. 

A  family  with  a  white  forelock  occurring  in  four 
generations  has  been  described  by  Holmes  and  Scho- 
field  (191 7).  This  lock  occurs  in  the  centre  of  the 
fore  part  of  the  scalp,  the  region  affected  being  quite 
small  (size  of  a  florin).  Heterozygous  females  do  not 
show  the  mark.  It  would  appear  that  the  character 
behaves  as  a  dominant  in  males  and  as  a  recessive  in 
females  (see  Fig.  11),  like  the  inheritance  of  horns 
in  crosses  of  a  breed  of  sheep  in  which  onh'  the  males 
have  horns  with  one  in  which  both  sexes  are  hornless. 
In  a  white  forelock  family,  described  by  Pearson, 
Nettleship,  and  Usher  in  the  monograph  on  albinism 

*  One  of  these  is  doubtful. 


62  HEREDITY  AND  EUGENICS 

in  man,  the  white  lock  occurred  only  in  males,  but 
was  transmitted  through  females,  skipping  a  generation 
in  each  case. 

A  much  more  interesting  and  extensive  pedigree 
of  a  white  lock  family  is  given  by  Miller  (191 5).  In 
this  familv  the  condition  has  been  traced  throucfh 
six  generations,  including  203  individuals.  Dr.  W.  B. 
Little,  whose  mother  is  known  to  have  had  the  lock, 
emigrated  from  Carhsle,  England,  to  New  Brunswick, 
Canada,  about  1824,  and  his  descendants  through 
four  generations  show  the  w^hite  lock  or  flare.  Some 
members  of  the  family  also  have  one  or  more  colour- 
less spots  on  their  bodies.  The  condition  behaves  as 
a  simple  dominant,  since  in  families  with  one  normal 


Fig.   II. — Family  showing  a  White  Forelock. 

and  one  marked  parent  the  num.bers  were  fifty-one 
normal  and  forty-five  with  the  flare  (where  equality 
would  be  expected) ;  and  where  both  parents  are 
norm.al  all  the  children  are  the  same.  This  family 
traces  its  origin  back  through  the  Percys  and  Morti- 
mers to  Edward  III.  That  the  white  lock  is,  at  least, 
as  old  as  the  family  of  Harrv  (Hotspur)  Percy  is 
know^n  b}^  the  tradition  that  the  white  lock  originated 
in  connection  with  his  death  at  the  battle  of  Shrews- 
bury in  1403.  When  the  news  of  his  death  reached 
his  wife,  she  is  said  to  have  swooned  and  to  have 
given  birth  shortly  afterwards  to  a  son  bearing  a 
white  patch  on  his  forehead.  One  member  of  the 
famity  has  found   from  other  records  that  the  patch 


PHYSICAL  CHARACTERS  IN  MAN         63 

goes  back  at  least  to  the  Percys.  It  happens,  also, 
that  Lad}^  Perc}^  was  an  albino.  The  white  flare 
may  therefore,  possibly,  have  originated  with  her, 
for  although  no  such  case  is  on  record,  it  is  known 
(see  next  paragraph)  that  spotted  mulattoes  arise 
from  an  ancestr\^  in  which  different  types  of  skin 
pigmentation  have  been  involved. 

Another  interesting  case,  first  recorded  by  Simpson 
and  Castle  (191 3),  is  of  spotting  arising  in  a  coloured 
race.  It  originated  as  a  novelty — a  spotted  woman 
born  from  ordinary  mulatto  parents  in  Louisiana  in 
1853.  No  case  of  spotting  had  previously  been 
known  in  that  part  of  the  country.  She  married 
a  normal  black  negro,  and  their  children  numbered 
fifteen,  eight  spotted  like  the  mother,  and  seven 
normal,  but  var3dng  in  depth  of  colour  as  is  usual  with 
mulattoes.  Three  of  the  normal  children  and  three 
spotted  married  normal  negro  mates.  The  normals 
had  in  all  seven  children,  all  normal.  The  spotted 
had  in  all  nine  spotted  and  two  normal.  This  indi- 
cates that  all  the  spotted  individuals,  male  and 
female,  behaved  as  heterozygotes,  and  that  complete 
segregation  occurs  between  spotting  and  non-spotting. 
The  fact  that  spotting  appears  rarely  and  sporadically 
among  the  innumerable  mulatto  crosses  tells  strongly 
against  it  being  the  result  of  an  inherited  spotting 
factor.  The  particularly  clear  evidence  here  indicates 
that  it  arises  as  a  mutation  in  the  h\'brid  stock,  the 
original  spotted  individual  being  heterozygous  and 
the  piebald  condition  dominant  to  normal  mulatto 
pigmentation. 

With  regard  to  the  ancestral  colour  of  man,  it  seems 
clear  that  the  most  primitive  races  were  black  (as 
John  Hunter  concluded  150  3^ears  ago),  or  at  any 
rate  dark,  as  the}^  are  now,  and  that  the  white  race 
arose  from  them  wdth  loss  of  pigmentation.  It 
appears  unlikely  that  a  simple  mutation  was  involved. 


64  HEREDITY  AND  EUGENICS 

Although  albino  mutations  occur  in  black  races,  the 
'  white  "  man  is  by  no  means  devoid  of  pigmentation. 
It  appears  probable  that  man}^  small  germinal  changes 
affecting  pigmentation  were  involved.  The  known 
relations  between  skin  pigmentation  and  the  adrenal 
capsules  indicate  that  germinal  changes  which 
affected  the  activity  of  these  glands  were  really  in- 
volved. From  recent  studies  of  the  endocrine  gland 
secretions,  it  appears  that  differences  in  the  activities 
of  various  endocrine  glands  are  responsible  not  only 
for  the  differences  in  pigmentation  of  the  various 
races  of  mankind,  but  also  for  their  characteristic 
physiognomies  (see  p.  211  ff.). 

In  the  same  way,  it  is  highly  probable  that  brown 
w^as  the  primitive  eye  colour  in  man,  and  that  blue 
arose  from  it  through  one  or  more  mutations,  with 
loss  of  pigment.  (For  a  further  discussion  of  this 
subject  see  p.  44.)  It  may  be  that  blue  arose  origin- 
ally as  a  simple  mutation  from  brown,  and  that 
intermediate  shades  have  come  in  later.  This  has 
been  shown  to  be  the  history  of  various  cases  of 
melanism  in  Lepidoptera.  But  at  present  there  is 
no  definite  evidence  to  prove  the  point  either  way  as 
regards  man.  When  blue  e3'es  were  once  established^ 
they  multiplied  in  the  northern  races,  perhaps  through 
sexual  selection,  until  blue  eyes  are  characteristic  of 
the  Scandinavian  and  other  northern  peoples.  But 
the  native  peoples  in  tropical  countries  appear  always 
to  have  retained  brown  e3^es,  the  pigment  probably 
being  a  protection  for  the  e3^e  against  the  strong  rays 
of  the  sun.  The  white  race  is  thus  in  a  sense  an 
albinotic  variation,  which  has  arisen  through  loss  of 
pigmentation.  This  loss  has  been  carried  still  further 
in  the  more  northern  races  with  fair  complexion, 
light  hair,  and  blue  e3^es. 

In  the  Pearson  monograph  on  albinism  many  early 
records  of  albinotics  are  considered.     It  is  concluded 


PHYSICAL  CHARACTERS  IN  MAN  65 

that  there  is  no  evidence  that  a  tribe  or  clan  of  albi- 
notics  ever  existed,  but  there  are  numerous  records 
indicating  the  existence  of  considerable  numbers  of 
albino  individuals.  In  connection  with  Dampier's 
expedition  to  Darien  in  1681,  there  is  a  long  and 
circumstantial  account  of  the  "  white  Indians,"  who 
could  see  better  by  moonlight,  etc.  I'here  is  a 
similar  record  for  Brazil  in  1775.  Cortez,  in  connec- 
tion with  the  Spanish  conquest  of  Mexico,  described 
Montezuma's  palace  as  containing  an  entourage  of 
albinos.  In  a  similar  w^ay,  in  the  Middle  Ages,  fools 
and  dwarfs  were  considered  a  desirable  accessor}-  to 
the  retinue  of  kings  and  nobles.  As  late  as  1841 
Catlin  described  a  "  white  Indian  tribe  "  in  Upper 
Missouri  containing  many  albinos.  It  appears  that 
albinism  is  now  most  frequent  among  the  Indians  of 
Arizona  and  Mexico.  Poole,  in  1872,  reported  light- 
haired  and  fair  Indians  from  Queen  Charlotte  Islands 
and  British  Columbia.  Newspaper  descriptions  led 
to  a  belief  in  a  colony  of  albinos  living  in  "  the  forest 
country  "  back  of  Cape  Cod,  Massachusetts,  but 
Pearson  could  get  no  definite  confirmation  that  such 
a  group  ever  existed,  although  it  may  have  had  some 
basis  in  fact. 

Albinism  is  known  in  most  races  and  probably 
occurs  in  all.  Its  frequency  is  unknown,  but  is  esti- 
mated at,  perhaps,  i  in  5,000  or  i  in  30,000.  In 
Germany,  out  of  nearly  four  million  children  dealt 
with,  about  400  had  "  w^hite  hair."  This  would  give 
a  frequency  of  i  in  10,000.  A  similar  proportion 
was  found  in  Norway.  Of  the  400  onl}'  32  had  "  red 
eyes,"  and  of  these  only  23  had  also  white  hair: 
hence  only  one  complete  albino  in  200,000,  but  the  true 
prevalence  may  be  greater.  In  Austria,  from  statis- 
tics of  insane  albinotics,  it  was  estimated  that  i  in 
400,  or  I  in  2,000,  of  the  population  were  albi- 
notics.    This    very    high    estimate    is    probably    due 

5 


66  HEREDITY  AND  EUGENICS 

to  correlation  between  albinism  and  mental  derange- 
ment. 

In  Scotland  loo  to  150  living  albinos  were  recorded 
from  about  half  the  population.  This  indicates  a 
frequency  of  i  in  every  15,000  to  25,000  inhabitants. 
Moreover,  less  satisfactory  records  are  available  from 
many  other  countries  and  races.  It  appears  that 
albinism  occurs  as  a  mutation  in  the  absence  of  cross- 
ing of  races,  both  in  the  dark  and  white  races,  but 
it  also  frequently  arises,  as  we  have  seen,  a  generation 
or  two  after  a  mixture  of  races  has  taken  place.  The 
piebald,  apparently  arising  only  from  cross-breeds, 
is  far  rarer  than  the  complete  albino. 

Pearson  also  considers  the  pathological  condition 
known  as  leucoderma  (white  patches  on  the  skin), 
and  finds  there  is  no  physiological  differentiation  from 
albinism,  the  two  being  distinguishable  only  by  the 
inheritance  of  the  latter.  Pearson  distinguishes 
between  spotlings  and  piebalds,  the  former  including 
those  wdth  white  miarkings  which  do  not  extend  to 
extensive  areas  on  the  trunk.  The  extent  of  the 
leucosis  is  probably  hereditary,  but  there  is  no  sharp 
line  between  spotlings  and  piebalds.  The  spothng 
of  one  generation  may  be  the  father  of  a  piebald  in 
the  next.  Albinism,  piebaldism,  and  leucoderma  are 
probably  all  to  be  accounted  for  by  the  same  meta- 
bolic defect.  Leucoderma,  however,  is  not  necessarily 
inherited. 

A  family  in  which  albinism  was  carried  as  a  reces- 
sive for  five  generations  is  described  by  Sedgwick 
(1861).  The  pedigree  of  this  famil}'  is  given  in 
Fig.  12.  One  of  the  original  great -grandparents 
must  have  been  carr3dng  albinism  as  a  recessive. 
The  wife  of  No.  II.  i  must  have  been  in  the  same 
condition.  Their  daughter,  Josephine  (III.  i),  was 
the  only  descendant  of  this  son  to  show  albinism. 
The  two  grandsons,  III.  2  and  III.  3,  married  sisters. 


PHYSICAL  CHARACTERS  IN  MAN         6- 

both  of  whom  evidently  carried  albinism  recessive. 
No.  III.  3  had  seven  normal  sons,  five  of  whom 
married,  but  only  one  of  them  had  albino  children. 
This  family  numbered  three  normal  sons,  and  nine 
daughters,  four  of  whom  were  albinos.  The  mother 
again  must  have  carried  albinism  as  well  as  the 
father,  if  the  condition  is,  as  usual,  a  strict  recessive 
(see  p.  70). 

In  another  record  of  Sedgwick,  two  grandsons  in 
a  Swiss  village  had  each  two  daughters,  one  normal 
and  one  albino.  The  albino  great-granddaughters 
married.     One   had   no    children,   the   other   had   an 


I 

n 

EL 

m 


D^O 


xO 


^'xU 


CF 


X    O 


O     X 


V 

Sisters 


^~^~^M, 


thery 
ch/ 


4     ^5    A-.6    r^7     j^e     J^9    J^IO    ^ 

xQ 


4*«*66660 


Fig.   12. — Pedigree  of  Albinism  in  a  Family. 


imperfect  albino  by  a  husband  with  black  hair  and 
brown  eyes.  There  was  probably  intermarriage  in 
both  these  lines  of  descent. 

Little  (1920)  mentions  that  a  piebald  coat  charac- 
terises such  breeds  of  dogs  as  foxhounds,  beagles, 
Boston  terriers,  St.  Bernards,  and  collies.  The 
spotting  reaches  an  extreme  in  bull  terriers  where 
normally  only  the  eyes  are  pigmented.  The  origin 
of  spotted  individuals  from  t3'pical  ancestors  is 
recorded  in  two  pure  breeds  of  pedigree  dogs,  and 
it  is  considered  that  they  may  have  arisen  through 
mutations.  In  the  first  a  spotted  female  was  born 
from    two    solid-coloured    pedigreed    and    registered 


68  HEREDITY  AND  EUGENICS 

Scottish  terriers,  but  since  a  certain  dog  occurs  in 
both  the  male  and  female  ancestral  lines  the  outcrop 
of  spotting  would  be  accounted  for  if  that  animal 
were  carr34ng  a  recessive  factor  for  spotting.  In  the 
other  case,  four  spotted  puppies  occurred  in  tw^o 
litters  of  pedigree  Airedale  terriers.  The  pedigree 
of  the  five  previous  generations  shows  that  one  male 
occurred  seven  times  and  one  female  three  times  in 
this  pedigree,  the  former  occurring  on  both  sides  of 
each  ancestral  line.  He  was  probably  carr3"ing  a 
recessive  factor  for  spotting,  or  possibly  a  mutation 
giving  rise  to  this  factor  took  place  in  his  gametes. 

The  wTiter  (Gates,  igoga)  found  in  a  cross  between 
a  pure-bred  Old  Enghsh  sheep  dog  and  a  Scotch 
collie  that  F^  dogs  were  produced  wdth  several  dif- 
ferent lengths  of  tail,  or  no  tail,  like  the  mother,  and 
with  many  other  differences  in  coat,  build,  and 
temperament.  It  is  probable  that  almost  all  our 
pedigree  breeds  of  domestic  animals  carr}^  some 
recessive  characters,  w^hich  have  never  been  eliminated 
since  the  original  crosses,  which  in  man}^  cases  w'ere 
the  foundation  of  the  breed.  But  these  germinal 
difi"erences  must  have  arisen  at  some  time  through 
germinal  changes  which  gave  rise  to  the  parental  t3^pes, 
although  similar  germinal  changes  may  equally  well 
occur  afterwards  and  be  carried  as  recessives  in  the 
germ  plasm  until  a  cross  or  inbreeding  brings  them  out. 

The  Pearson  monograph  includes  also  a  study  of 
peculiarities  of  vision,  such  as  night-blindness,  as 
well  as  the  hair,  of  albinotics,  and  also  albinism  in 
various  animals.  Complete  albinos  wdth  pink  eyes 
are  known  to  occur  in  "  pure  "  races  of  man,  just 
as  they  occur  in  many  mammals,*  birds,  and  plants 

*  There  are  records,  for  example,  of  albino  beavers,  chipmunks 
{Tamias),  squirrels,  woodchucks  {Arctomys),  robins  {Turdus 
migratorius\  and  sparrows.  Dean  (1903)  says:  "True  albinos 
occur    among    hag-fishes,    and    partial    albinos    are    not    rare." 


PHYSICAL  CHARACTERS  IN  MAN         69 

(white  petals).  The  monograph  above  mentioned 
also  includes  a  study  of  seasonal  variation  in  animals 
that  are  white  in  winter,  such  as  Lepus  variabilis  in 
Scotland.  Crosses  of  white  and  black  Pekinese  does 
are  also  believed  to  furnish  evidence  of  the  de  novo 
origin  of  spotting  and  blends.  It  is  well  knr^wn, 
of  course,  that  in  certain  breeds,  as  the  Dalmatian, 
particular  types  of  spotting  have  become  a  fixed 
characteristic  of  the  breed.  Numerous  Mendelian 
studies  of  spotting  in  mammals  have  been  made  in 
recent  years,  especially  in  rabbits,  rats,  and  mice, 
and  complicated  theories  of  inheritance  of  spotting 
have  been  formulated.  The  subject  is  complex  and 
far  from  settled,  but  it  seems  clear  that  in  man}^  cases 
degrees  of  spotting  and  their  inheritance  can  be 
explained  on  the  basis  of  a  series  of  factors  for  spotting. 
The  evidence  clearly  indicates,  I  think,  the  sporadic 
de  novo  origin  of  spotting  in  man,  but  it  does  not 
follow  that  the  same  is  necessarily  true  for  dogs.  In 
some  breeds  spotting,  however  attained,  has  the  status 
of  a  germinal  factor,  and  the  regularity  with  which 
white-black  crosses  of  Pekinese  yield  definite  patterns 
would  seem  to  indicate  another  mode  of  heredity 
behaviour — i.e.,  that  a  spotting  or  pattern  factor  is 
present  in  these  crosses. 

Detlefson  (1920)  has  described  a  herd  of  albino 
cattle  on  a  farm  in  Minnesota  with  several  points  of 
interest.  This  herd  originated  from  two  albino 
calves — a  bull  and  a  heifer — which  resulted  from 
mating  a  "  full-blooded  "  Holstein  bull  with  "  grade  " 
Holstein  cows.  The  parents  had  the  normal  black- 
and-white  spotted  coat  colour,  while  the  calves  were 


Standley  (192 1)  refers  to  an  early  American  record  of  an  albino 
black  bear  with  "  four  cubs,  one  white,  with  red  eyes  and  red 
nails,  like  herself,"  showing  that  albinism  must  have  been 
carried  as  a  recessive  in  the  strain. 


70  HEREDITY  AND  EUGENICS 

pure  white  with  pink  eyes.  The  original  bull  produced 
these  two  albinos  out  of  matings  with  about  twenty 
grade  Holstein  cows,  the  remaining  calves  being  nor- 
mal. Unfortunately  the  original  records  of  the  herd 
were  destroyed  by  fire,  for  the  later  breeding  behaviour 
of  these  two  albinos  is  peculiar.  FYom  its  manner 
of  origin  one  would  expect  the  albinism  to  be  present 
as  a  recessive  character  in  the  germ  plasm  of  this 
herd.  But  the  young  albino  bull  mated  to  grade 
Holstein  cows  produced  only  albino  offspring — about 
twent}^  in  number.  The  albinos  mated  inter  se, 
moreover,  produced  only  albinos,  and  four  albino  cows 
mated  to  a  registered  Holstein  bull  (the  original  bull 
had  been  killed)  produced  three  albinos  and  one 
normal.  It  is  not  certain  from  these  later  matings 
that  the  albinism  behaved  as  a  simple  dominant, 
for  there  is  no  record  of  coloured  offspring  from  two 
albino  parents.  But,  at  any  rate,  the  later  hereditary 
behaviour  is  different  from  that  at  the  time  of  its 
original  appearance  as  a  mutation,  and  it  is  not  clear 
that  this  change  in  behaviour  can  be  explained  merely 
as  a  reversal  of  dominance. 

The  albinos  showed  no  pigment  in  the  skin,  eyes, 
horns,  or  hoofs,  except  in  one  cow  which  had  a  small 
black  spot  about  one  centimetre  square  in  one  ear. 
There  was  no  alteration  in  milk-production,  but  the 
albinos  were  extremely  sensitive  to  light,  and  grazed 
listlessly  during  the  day  with  partly  closed  eyes. 
Such  albinos  are,  of  course,  quite  different  from  the 
famous  Chilhngham  and  Chartley  herds  and  other 
races  of  w^hite  cattle.  The  evidence  indicates  that 
in  these  the  white  is  a  dominant,  and  that  they  are 
descended  from  original  prehistoric  wild  white  cattle 
in  Britain  (see  Storer,  1881,  and  MacDonald  and  Sin- 
clair, 1882).  The}^  are  not  pure  white,  but  had  typi- 
cally black  hoofs  and  muzzle,  a  circle  round  the  eyes, 
black  tips  to  the  horns,  and  in  some  cases  a  black  tip 


PHYSICAL  CHARACTERS  IN  MAN         71 

to  the  tail.  Wild  white  cattle  from  Thessah',  etc., 
were  also  known  to  the  Greeks  and  Romans,  and  in 
ItRly  a  white  breed,  in  which  the  calves  are  yellowish, 
continues  down  to  the  present  time. 

Three  types  of  albino  horses  have  recently  been 
described  (Wriedt,  191 8)  in  two  Norwegian  breeds. 
The  heterozygous  condition  is  intermediate  in  these 
horses,  and  albinism  appears  to  behave  nearly  the 
same  as  in  guinea-pigs. 

Civilisation  has  often  been  credited  with  the  pro- 
duction of  the  numerous  congenital  deformities  that 
appear  in  man.  But  various  studies,  such  as  that  of 
Stannus  (i 914)  on  the  Bantus  of  Nyasaland,  show  that 
the  same  abnormalities  continue  to  appear,  probably 
with  equal  frequency,  in  native  races,  even  though 
the  more  marked  of  them  are  ruthlessly  eliminated 
by  infanticide.  It  is  evident  that  the  conditions  of 
civilisation  tend  rather  to  preserve  than  to  originate 
abnormalities,  and  that  natural  selection  in  native 
races,  as  in  wild  animals,  combined  with  parental 
selection,  tends  to  eliminate  individuals  possessing 
characters  which  place  them  at  a  disadvantage  in 
the  struggle  for  existence. 

A  short  account  is  published  (Thadani,  1921)  of  a 
Hindu  Amil  community  in  India,  in  which  a  toothless 
type  of  man  occurs.  The  men  are  not  only  toothless, 
but  bald-headed  and  extremely  sensitive  to  heat. 
The  evidence,  so  far  as  it  goes,  indicates  that  the 
character  is  sex-hnked.  Anodont  females  are  not  at 
present  known,  but  if  daughters  of  a  toothless  father 
are  married  to  a  normal  man,  their  male  children  are 
toothless  (Bhudas). 

Left-handedness. 

Another  innocuous  feature  whose  inheritance  is 
well  known  is  left-handedness,  which  the  results  of 
Jordan  (191 1)  and  of  Hurst  {1912)  indicate  is  inherited 


72  HEREDITY  AND  EUGENICS 

as  a  simple  Mendelian  recessive  character,  at  least  in 
some  families.  Ramale}^  (191 3)  came  to  the  same 
conclusion,  based  on  1,740  cases.  He  estimated  that 
the  condition  is  carried  in  about  one-sixth  of  the 
population.  Left-handedness,  as  a  character,  may 
bear  some  resemblance  to  reversed  symmetry  in 
certain  Gastropods.  This  reversal  has  been  shown 
by  Conklin  to  begin  in  development  with  the  cleavage 
of  the  ^%%,  the  spiral  cleavage  being  dextral  in  one 
case  and  sinistral  in  the  other,  but  its  inheritance  is 
unknown.  Ambidextrous  individuals  in  man  appear 
to  have  inherited  left  -  handedness  and  acquired 
dexterity  with  the  right  hand.  There  are  apparent 
exceptions,  how^ever  (see  Compton,  191 2,  where  a 
number  of  references  will  be  found),  as  in  a  family 
quoted  by  D.  J.  Cunningham  in  the  Journal  of  the 
Anthropological  Institute,  xxxii.,  1902,  from  Aime 
Pere,  where  a  left-handed  mother  and  a  right-handed 
father  had  eight  sons  and  six  daughters,  all  left- 
handed.  If  the  father  were  heterozygous,  this  result 
would  be  possible,  though  very  improbable,  even  if 
left-handedness  were  regarded  as  a  recessive.  It 
would  seem  more  probable  that  in  such  a  case  the 
dominance  has  been  reversed.  There  is  also  clear 
evidence  that  in  certain  families  the  condition  is 
sex-linked. 

A  recent  paper  by  Beeley  (1920)  considers  left- 
handedness  from  various  points  of  view,  and  gives 
a  number  of  references  to  the  literature  of  the  subject. 
Estimates  of  the  frequency  of  left-handedness  have 
varied  between  6  and  2  per  cent.,  wdth  4  per  cent, 
as  the  medium  frequency.  This  applies  to  American 
Indians  (Apaches  and  Pimas),  as  well  as  to  white 
races.  That  the  condition  is  more  frequent  in  man 
than  in  woman  has  been  affirmed  and  denied.  Some 
have  found  it  more  frequent  among  delinquents  and 
among  negroes,  but  there  seems  to  be  no  sufficient 


PHYSICAL  CHARACTERS  IX  MAN  73 

basis  for  these  conclusions.  Jordan,  from  an 
examination  of  700  university  students,  1,394 
coloured  school  children,  and  668  others,  concludes 
that  the  condition  is  inherited,  but  is  not  very  clear 
that  it  follows  Mendelian  principles.  Baldwin  f(jund 
that  the  tendency  to  use  one  hand  more  than  the 
other  developed  about  the  seventh  month  after  birth, 
when  all  influences  to  the  greater  use  of  one  hand 
were  ehminated.  The  old  idea  that  right-handedness 
was  developed  because  warriors  held  the  shield  with 
their  left  hand  to  protect  their  heart  and  wielded  the 
spear  with  their  right  will  not  bear  analysis  with 
modern  conceptions.  That  right-  or  left-handedness 
does  not  depend  on  a  difference  in  the  eyes  is  also 
shown  by  the  fact  that  there  is  the  same  proportion 
of  left-handed  among  the  congenitally  blind  as  among 
those  who  use  their  eyes. 

Beeley  considers  the  results  from  106,356  children 
examined,  and  concludes  that  all  degrees  exist  from 
extreme  left-handedness  to  extreme  right-handedness. 
Among  this  number  of  children  were  found  fort}'- 
two  "  mirror- writers."  The  results  showed  that 
mirror- writing  is  not  necessarily  correlated  with 
mental  deficiency,  but  rather  it  is  characteristic  of 
extreme  left-handedness.  A  method  was  devised 
for  measuring  the  degree  of  left-handedness  by  means 
of  a  brass  plate  divided  into  squares,  on  which  two 
straight  lines  at  right  angles  to  each  other  were  to  be 
traced.  The  squares  were  alternately  insulated  in 
such  a  way  that  ever}^  error  produced  an  electric 
current  which  was  recorded  in  a  counter.  The  number 
of  errors  in  tracing  the  two  lines,  multiplied  by  the 
time  taken,  was  used  as  a  measure  of  the  degree  of 
left-handedness.  Obviously  general  dexterity  would 
play  an  important  part  in  a  result  of  this  kind,  and 
the  age  of  the  child  would  be  an  important  element  in 
such  a  result.     It  is  not,  therefore,  clear  that  the  degree 


74  HEREDITY  AND  EUGENICS 

of  left-handedness  forms  such  a  continuous  series  as 
these  resuhs  would  indicate,  although  it  is  highly 
probable,  if  not  certain,  that  degrees  of  left-handed- 
ness exist .  Beeley  suggests  that  a  slightly  left-handed 
child  should  be  taught  to  use  its  right,  but  that  an 
extreme  left-hander  should  not. 

That  the  right  hemisphere  of  the  brain  controls 
the  left  side  of  the  body  and  vice  versa  is,  of  course, 
well  known ;  also  that  the  development  of  the  speech- 
centre  may  be  interfered  with  by  a  too  early  attempt 
to  teach  a  left-handed  child  to  use  its  right  hand, 
thus  leading  to  stuttering. 

The  manner  of  clasping  the  hands,  whether  right- 
handed  or  left-handed — i.e.,  with  the  right  thumb 
over  the  left  or  vice  versa — although  characteristic 
enough  for  the  individual,  apparently  bears  no 
relation  to  right  or  left-handedness.  It  does  not 
follow  any  known  rule  of  inheritance,  but  appears, 
nevertheless,  to  be  partially  inherited,  for  when  both 
parents  show  a  right-  or  left  -  handed  clasp  the 
majority  of  the  children  will  be  of  the  same  t3^pe. 
Statistics  show  that  en  masse  the  two  methods  usually 
occur  with  equal  frequenc}',  but  neither  condition 
breeds  true.  Compton  (191 2)  has  studied  the  right 
and  left-handed  seedlings  (as  regards  the  manner  of 
folding  of  the  first  leaf),  which  occur  in  various  cereals, 
but  the  condition  is  not  inherited.  Thus  the  seeds 
from  a  left-handed  (LH)  plant  produce  the  same 
ratio  of  LHand  RH  plants  as  do  the  seeds  of  a  right- 
handed  (RH)  plant.  In  two-rowed  barley  this  ratio 
LH/RH  was  shown  to  be  constant  for  three  genera- 
tions, and  therefore  inherited.  In  a  total  of  19,165 
seedlings,  the  percentage  of  LH  seedlings  =58-362. 
Seeds  planted  from  the  odd  and  even  rows  separately 
also  gave  the  same  preponderance  of  left-handed 
plants.  Six-rowed  barley  gave  a  similar  excess  of 
LH  plants.     In  oats,  however,  there  is  regularly  an 


PHYSICAL  CHARACTERS  IN  MAX  75 

excess  of  RH  plants  (LHr^44-88  per  cent.)-  This 
difference  may  have  some  connection  with  the  fact 
that  the  leaf-blades  of  barley  "  are  generally  slightly 
twisted  into  a  right-handed  screw,  while  in  oats  the 
torsion  is  in  the  reverse  direction."  In  maize,  again, 
there  is  no  inheritance  of  left-handedness  or  right- 
handedness  as  such,  but  the  seeds  in  odd  rows  give 
an  excess  of  RH,  those  from  even  rows  an  equal  excess 
of  LH  seedlings.  The  ratios  were  54-22  per  cent,  and 
46-16  per  cent.  LH  respectively.  Thus,  the  total 
numbers  of  LH  and  RH  seedlings  from  a  cob  are 
practically  equal.  Compton  suggests  that  the 
differences  between  row^s  in  this  regard  may  perhaps 
be  accounted  for  by  unequal  pressure  on  the  embryos. 
In  any  case  it  is  a  relief  to  find  something  which  is 
definitely  not  inherited.  The  question  of  the  limits 
of  human  inheritance  will  be  discussed  in  a  later 
chapter. 

In  1908  a  list  of  normal  and  abnormal  features 
in  man,  whose  inheritance  had  been  studied,  was 
published  by  Hurst,  and  Bateson  (1909)  devoted  a 
chapter  to  this  subject.  Davenport  (191 2)  also  con- 
sidered many  cases,  and  Biomeirika  contains  masses 
of  statistical  data  on  the  inheritance  of  various 
features.  Abnormalities  are  frequently  inherited  as 
dominants,  and  they  probably  originated  as  mutations. 
Such  are  hexadactyly,  brachydactyly,  "  lobster  claw," 
some  forms  of  cataract,  keratosis,  congenital  stationary 
night-blindness  (in  certain  famiUes),  and  many  others. 
Brittleness  of  bones  or  osteopsathyrosis  (Conard  and 
Davenport,  191 5)  is  a  remarkable  congenital  weakness 
which  appears  to  be  inherited  as  a  dominant  character. 
In  one  recorded  case  a  boy  suffered  at  least  twelve 
fractures  of  his  limbs  before  reaching  the  age  of  three 
years,  being  born  with  both  thighs  broken.  Later 
this  extreme  liability  to  fracture  began  to  diminish, 
but  that  it  may  still  remain  a  serious  defect  in  the 


76  HEREDITY  AND  EUGENICS 

adult  is  shown  by  the  fact  that  the  mere  tension  of  the 
muscles  or  weight  of  the  body,  as  in  dancing,  may  be 
sufficient  to  cause  a  fracture.  Twins  may  be  born 
in  families  having  the  peculiarity,  one  showing  the 
defect  and  the  other  normal.  Sedgwick  (1863)  cites 
a  family  from  Dr.  Pauli  with  a  less  extreme  form  of 
the  condition,  in  which  the  brittleness  was  confined 
to  the  bones  of  the  upper  extremities.  It  occurred  in 
three  generations. 

Digital  Abnormalities. 

We  may  now  consider  some  of  the  digital  peculiari- 
ties whose  inheritance  has  been  studied  in  man. 
A  very  good  case  is  that  of  split  hand  and  foot,  or 
"  lobster  claw."  Lewis  and  Embleton  (1908)  consider 
a  collection  of  180  cases  of  this  deformity.  They  find 
it  by  no  means  uncommon.  Many  varieties  of  the 
condition  occur.  In  the  "  G  "  family,  to  which  many 
of  their  data  refer,  the  hands  are  variously  misshapen, 
and  each  foot  consists  of  two  toes  separated  by  a 
deep  cleft.  Rarely  the  toe  on  one  side  may  be  double, 
and  the  toes  are  generally  bent  claw-wise  at  their 
extremities.  Both  the  hands  and  feet  of  these  people 
are  said  to  have  great  functional  capacity  and 
accuracy  in  use,  including  needlework  and  hand- 
writing. The  variations  in  the  deformity  are  only 
in  degree.  Rarely  one  or  both  hands  ma}^  be  normal 
when  the  feet  are  split.  The  condition  may  also  be 
associated  with  syndactyly  (fused  fingers)  or  Poly- 
dactyly (extra  fingers  or  toes).  Cross  bones  frequently 
occur  in  the  hands,  but  never  in  the  feet.  The  in- 
heritance is  essentially  that  of  a  Mendelian  domi- 
nant, though  the  expected  ratios  are  not  always 
adhered  to. 

In  the  "  G  "  family  this  condition  has  been  traced 
through  five  generations.     It  never  skips  a  generation. 


PHYSICAL  CHARACTERS  IN  MAX  -j-j 

and  derived  normals  x  normals  crive  only  normal 
offspring.  It  is  transmitted  equally  through  either 
sex.  In  the  offspring  of  crosses  between  deformed 
and  normals,  Lewis  and  Embleton  find  a  total  of 
forty-four  deformed  to  thirty-two  normal.  In  some, 
though  not  all,  of  the  other  data  of  inheritance  of  split 
foot,  they  find  a  similar  excess  of  deformed  individuals, 
w^hich  appears  to  be  significant.  It  does  not  neces- 
sarily follow  that  the  condition  is  not  represented  by 
a  single  difference  in  the  germ  plasm.  Indeed,  they 
agree  that  it  has  arisen  as  a  "  sport  "  or  mutation 
of  germinal  origin.  They  state  "  there  are  records  of 
over  thirty  instances  of  the  origin  of  this  same  sport," 
and  account  for  this  by  the  now  widely  accepted  view 
that  mutations  tend  to  occur  and  recur  in  definite 
directions.  Since  the  character  is  dominant  it  cannot 
remain  hidden  in  the  germ  plasm,  but  must  appear 
externally  if  the  germ  cell  containing  it  develops  into 
an  individual. 

All  writers  agree  that  this  character  segregates 
sharply,  but  they  claim  that  it  "  does  not  follow  the 
laws  of  Mendel,"  because  of  the  excess  of  abnormals 
in  the  offspring  of  crosses  with  normals.  This  does 
not  necessarily  follow,  for  it  is  now  known  that  many 
physiological  and  environmental  conditions  may  cause 
distortion  of  Mendelian  ratios.  Lewis  and  Embleton 
beheve  there  is  a  "  decided  tendency  for  the  de- 
formity to  die  out  "  in  later  generations.  They 
appear  to  think  that  this  results  from  the  germinal 
condition  representing  split-foot  becoming  unstable. 
Perhaps  the  struggle  for  existence  has  something  to 
do  with  it,  as  well  as  sexual  selection. 

Pearson  (1908)  refers  to  the  evidence  for  the 
existence  in  Scotland  of  a  family,  "  the  Cleppie  Bells," 
with  a  deformed  hand  inheritance  extending  over 
two  centuries.  He  traces  the  deformity  in  another 
family  for  four  generations,  and  finds  again  an  excess 


78  HEREDITY  AND  EUGENICS 

of  abnormals  in  the  offspring  of  crosses  with  normals 
(25  :  14).  He  concludes,  "  on  the  whole,  w^hile  these 
cases  give  ver}-  definite  evidence  of  the  segregation 
factor,  the}^  do  not  seem  to  me  to  favour  the  segrega- 
tion in  rigid  Mendelian  proportions."  The  stock  of 
this  family  is  otherwise  normal,  and  the}^  have  no 
difficulty  in  finding  normal  mates.  The  gait  is  un- 
gainl}^,  but  the  children  at  school  hold  their  own  in 
writing,  drawing,  and  needlework.  Additional  data 
for  this  family  are  given  by  McMullen  and  Pearson 
(191 3),  the  numbers  of  abnormals  recorded  having 
increased  from  twenty-five  to  thirty-three.  In  the 
third  generation  the  result  is  in  conformity  with  the 
Mendelian  expectation  of  equality  of  normals  and 
abnormals.  In  the  fourth  and  fifth  generations  there 
is  a  total  of  twenty-eight  affected  to  thirteen  normal. 
Ever3'thing  considered,  it  seems  most  reasonable  to 
regard  the  condition  as  due  to  a  single  Mendelian 
dominant  factor  which  arises  from  time  to  time  as 
a  mutation,  but  which,  through  increased  viability 
or  for  some  other  reason,  occurs  in  more  than  50  per 
cent,  of  the  offspring  from  crosses  with  the  normal. 
Lewis  (1909a)  records  certain  other  split-foot  pedi- 
grees. The  only  facts  that  need  specially  concern 
us  are :  (i)  a  family  of  ten,  in  w^hich  half  are  abnormal 
and  half  normal;  (2)  a  family  of  six,  all  abnormal. 
In  the  latter  the  father  may  perhaps  have  been 
homozygous. 

Brachydact3dy  is  an  abnormality  which  has  been 
even  more  studied  in  recent  3^ears,  although  it  is 
probabty  much  less  frequent  in  its  occurrence  than 
split-foot.  The  condition  is  illustrated  in  Fig.  13, 
which  shows  normal  and  brachydactylous  hands  for 
comparison,  and  Fig.  14,  w^hich  is  a  radiogram  showing 
the  bones  of  a  brachydact^dous  hand.  The  earliest 
stud}^  of  the  inheritance  of  brachydactyly  was  by 
Farabee     {1905)     in     an     American     family     from 


PHYSICAL  CHARACTERS  IN  MAN  79 

Pennsylvania.  He  shows  that  the  condition  was 
inherited  as  a  simple  Mendelian  dominant,  the  off- 
spring of  the  affected  mated  wdth  normal  giving 
50  per  cent,  of  each  type  (thirty-six  affected,  thirty- 
three  normal).  Brachydactylous  w^omen  cannot  play 
the  piano  well  owing  to  their  inability  to  span  the 
octave.  Brachydactylous  men  in  this  family  include 
farmers,  mechanics,  business  men,  and  school  teachers. 
One  was  head  of  a  commercial  school  and  a  fine  pen- 


FiG.    13. — Brachydactylous  and  Normal  Hands   for 
Comparison.     (After  Drinkwater.) 

man,  another  was  a  baseball  catcher.  The  arms  and 
legs  are  short,  but  the  sitting  height  is  nearly  normal, 
and  abnormals  are  stouter  than  their  normal  sibs.* 
There  is  an  unverified  tradition  in  the  family  that  the 
first  member  with  short  fingers  came  from  Normandy 
in  the  army  of  William  the  Conqueror.  Brachy- 
dactylous individuals  have  never  intermarried;  but 
the  abnormals  always  marry  first,  and  will  soon 
have  gained  a  generation  in  this  way.     This  was  the 

*  That  is,  brothers  and  sisters. 


8o 


HEREDITY  AND  EUGENICS 


first    case    of    Mendelian    inheritance    demonstrated 
in  man. 

Drinkwater  (1908)  independently  investigated  a 
British  family,  with  the  same  results  as  regards 
inheritance.  He  found  that  the  strength  of  grip  in 
brachydactylous  individuals  was  considerably  below 


Fig.  14. — Radiogram  of  a  Brachydactylous  Hand,  showing 
THE  Two  Phalanges  in  Each  Finger.     (After  Drinkwater.) 


the  average.  They  complain  that  they  cannot  play 
the  piano  or  any  other  musical  instrument  requiring 
normal  length  of  fingers,  their  grasp  of  objects  is 
smaller  than  normal,  and  the  women  cannot  do 
netting.  That  they  are  handicapped  is  shown  by  the 
fact  that  their  social  position  is  lower  than  that  of 


PHYSICAL  CHARACTERS  IN  MAN  8i 

their  normal  relatives.  They  are  engaged  in  un- 
skilled labour,  while  their  normal  relatives  include 
farmers,  grocers,  etc.  In  a  wild  tribe  where  personal 
defence  with  weapons  is  a  necessity,  brachydactylous 
individuals  would  probably  not  survive. 

In  several  papers  Drinkwater  has  made  a  careful 
anatomical  investigation  of  brachydactylous  hands 
and  feet,  including  radiographic  studies.  The  con- 
dition applies  equall}^  to  fingers  and  toes,  and  is 
accompanied  by  short  stature.  In  the  digits  he 
showTd  that  the  middle  phalanx  is  very  short,  and 
has  become  ankvlosed  to  the  base  of  the  terminal 
phalanx.  Hence  the  second  phalanx  is  rudimentary, 
and  at  a  certain  stage  of  development  it  unites  with 
the  terminal  phalanx.  The  most  important  feature 
is  the  absence  of  the  epiphysis  (terminal  cartilage, 
which  becomes  ossified)  at  the  base  of  the  second 
phalanx.  The  epiphysis  may  also,  perhaps,  be 
missing  in  some  cases  from  the  third  phalanx,  the 
second  and  third  phalanges  consisting  at  first  of  a 
single  piece  of  cartilage.  The  metacarpal  (wrist) 
bones  are  also  more  or  less  abnormal,  but  the  meta- 
tarsal (instep)  bones  are  unaffected.  This  abnormal 
f amity  was  ver}^  prolific,  the  number  of  children  in 
nine  families  averaging  eleven  each .  A  normal  woman 
had  forty-five  descendants,  while  a  brachydactylous 
woman  in  the  same  famity  had  ninety-nine  descendants . 
The  numbers  in  successive  generations  show  that  the 
condition  is  on  the  increase,  and  that  there  is  no 
chance  of  it  becoming  extinct  so  long  as  the  brachy- 
dact^dous  members  continue  to  marry.  For  some 
unknown  reason  the}^  do  marry  more  frequently  than 
their  normal  sisters. 

The  essential  feature  in  brach3^dact3dy  is,  then,  the 
absence  of  the  epiphysis  at  the  base  of  the  second 
phalanx,  with  subsequent  ankylosis  of  the  second  and 
third   phalanges.      The    fingers    are    about    half    the 


82  HEREDITY  AND  EUGENICS 

normal  length.  Although  brach3'dactylous  individuals 
are  lacking  in  some  forms  of  dexterity,  and  therefore 
must  accept  a  lower  social  status,  yet  they  show  a 
decided  increase  in  fecundity  compared  with  normal 
members  of  the  same  family.  In  this  family  twenty- 
five  now  living  in  England  and  Wales  are  brach}^- 
dactylous.  Beginning  with  the  fourth  generation,  the 
total  number  of  descendants  from  DR  x  RR*  crosses 
is  seventy-five,  of  whom  thirty-nine  are  abnormal. 

No  connection  could  be  traced  between  Drink- 
water's  first  brachydactylous  family  and  the  one 
described  by  Farabee,  there  being  no  surname  common 
to  the  two  families.  Drinkwater  (191 5)  has  since 
described  another  family,  how^ever,  which  he  has 
shown  to  be  descended  from  a  member  of  Farabee 's 
familv,  who  removed  from  America  and  settled  in  this 
country.  In  this  family  and  its  American  ante- 
cedents the  abnormality  can  be  traced  for  six  genera- 
tions. In  both  branches  of  this  family  the  proportion 
of  females  among  the  abnormals  is  exactly  61  per  cent. 
In  the  English  branch  fifty  abnormals  were  recorded 
to  forty-eight  normals,  where  50  per  cent,  of  each 
type  were  expected,  showing  that  heterozygous 
brachydactyls  produce  the  two  types  of  germ  cells  in 
equal  numbers.  Normals  mated  together  invariably 
have  only  normal  offspring.  The  shortness  of  stature 
of  brach3^dactyls  is  shown  to  be  due  to  the  short  legs, 
both  femur  and  tibia  being  shorter  than  in  normal 
members  of  the  family. 

Drinkw^ater  has  also  described  in  two  families  the 
condition  which  he  calls  minor  brachydactyly  (191 2, 
1 91 4).  In  a  Lancashire  famil}^  this  abnormality  has 
been  traced  through  five  generations,  and  sixteen 
abnormals  were  living  when  the  study  was  made. 
The  fingers  are  less  shortened  than  in  brachydactyly, 

*  D=dominant,    R=recessive,    hence   DR   is    a    heterozygous 
dominant. 


PHYSICAL  CHARACTERS  IN  MAN         83 

but  the  middle  phalanx  of  each  finger  is  abnormally 
short.  This  is  partly  due  to  the  absence  of  the 
epiphysis  from  the  base  of  the  second  phalanx, 
except  in  the  thumb  and  middle  finger,  and  also  to 
a  slight  shortening  of  the  second  phalanx,  but  is 
chiefly  due  to  the  fact  that  the  cartilage  between  the 
shaft  and  the  epiphysis  becomes  prematurely  ossified, 
thus  causing  cessation  of  growth  in  length  of  the 
fingers  at  an  early  age.  Ankylosis  of  the  epiphysis 
and  the  second  phalanx  frequently  occurs  earlier  in 
the  first  and  fourth  fingers  than  in  the  second  and 
third,  thus  leading  to  a  greater  shortening  of  the 
former.  The  abnormality  of  the  toes  is  practically 
identical  with  that  in  ordinary  brachydactyly.  This 
family  is  also  shorter  in  stature.  As  in  the  brachy- 
dactylous  family,  the  women  are  4I  inches  and  the 
men  8  inches  shorter  than  their  normal  siblings.  A 
total  of  twenty-one  abnormals  to  twenty-six  normals 
were  recorded  in  families  having  one  abnormal 
parent.  The  abnormals  in  this  family  are  said  to 
have  better  health  than  the  normals.  In  the  children 
the  abnormality  is  inconspicuous,  and  is  sometimes 
detected  only  by  flexing  the  finger. 

In  the  second  family  showing  minor-brachydactyly 
(Drinkwater,  191 4),  the  conditions  closely  resemble 
those  in  the  previous  family,  but  so  far  as  the  records 
go  back  there  is  no  connection.  It  is  found  in  five 
generations,  there  being  nine  abnormals  to  ten 
normals,  eight  of  the  former  now  living.  They  are 
all  descended  from  an  illegitimate  daughter  of  a  short- 
fingered  man,  the  mother  having  been  married  to  a 
normal  man  by  whom  she  had  entirely  normal  descen- 
dants .  These  forms  of  brachydactyly  are,  therefore,  all 
simple  Mendelian  dominants  like  split-foot,  but  they 
show  no  appreciable  excess  of  abnormals  in  inheritance, 
and  they  show  a  clear  tendency  to  increase  rather 
than  die  out,  notwithstanding  their  social  handicap. 


84  HEREDITY  AND  EUGENICS 

or  possibly  on  account  of  it.  Bateson,  who  discussed 
the  earher  records  of  brachydactyly  (1909,  p.  210), 
refers  to  a  four-generation  pedigree,  described  by 
Walker,  of  what  appears  to  be  a  mild  form  of  minor- 
brachydactyly  inherited  in  the  same  way. 

Lewis  (1909c),  in  a  thesaurus  of  the  results  of  the 
study  of  brachydactyly,  up  to  the  time  his  paper 
appeared,    cites     two    other    cases    with    interesting 


Fig.  15. — Hand  showing  Abnormal  Segmentation  op'  the 
Index  and  Middle  Fingers.     (After  Drinkwater.) 

features.  In  Mercier's  case  a  French  family  is 
described  in  which  eighteen  members  in  three 
generations  are  brachydactyl,  having  two  phalanges 
on  all  the  fingers  and  toes.  Hasselwander's  case 
(a  German  family)  presents  a  feature  of  special 
interest.  There  w^ere  six  abnormal  members  of  the 
family  in  three  generations.  The  original  brachy- 
dactyl of  this  pedigree  came  from  normal  parents. 
His  advent  must,  then,  mark  an  independent  origin  of 


PHYSICAL  CHARACTERS  IN  MAN 


8; 


the  condition  through  a  mutation,  unless  possibly  his 
affected  parent  only  had  the  condition  in  a  slight 
degree,  and  so  was  mistaken  for  a  normal.  The 
actual  origin  of  such  a  case  is  naturally  difficult  to 
prove,  and  this  can  only  be  done  where  the  conditions 
in  both  parents  and  grandparents  are  accurately  and 
certainly  knowai  from  observation  to  be  normal. 


Fig.  i6. — Radiograph  of  the  Two  Hands  of  a  Girl  Aged 
Nineteen,  in  the  Same  Family  as  Fig.  15.  (After 
Drinkwater.) 


That  various  other  modifications  of  typical  brachy- 
dactyly,  in  addition  to  those  described  above,  are 
inherited  in  the  same  way  is  shown  b}^  such  records 
as  those  recently  published  by  Dr.  Drinkwater  (191 6), 
whose  accurate  work  in  recording  these  cases  is  of 
great  value.  He  traces  through  four  generations  a 
case  of  abnormal  segmentation  of  the  index  and  middle 
fingers,  the  third  finger  being  much  longer  than  any 


86  HEREDITY  AND  EUGENICS 

of  the  others  owing  to  the  great  length  of  its  proximal 
phalanx.  The  first  and  second  fingers  are  also  more 
or  less  tilted  away  from  the  thumb  (see  Figs.  15  and 
1 6) .  There  are  thirty-six  descendants  of  the  abnormal 
members  of  the  family,  fifteen  of  whom  show  the 
abnormality.  The  feet  in  these  individuals  show 
ordinary  brachydactyly.  From  a  careful  study  of 
radiographs  the  following  anatomical  interpretation 
emerges :  The  index  finger  has  at  its  base  an  extra 
triangular  bone  which  sets  the  finger  obliquely  to  the 
hand.  The  proximal  phalanx  of  the  middle  finger 
appears  to  be  divided  equally  or  unequally  into  two 
parts;  the  lower  part,  however,  is  probably  an  extra 
bone  corresponding  to  that  in  the  index  finger,  and  it 
also  is  set  somew^hat  obliquety.  In  the  adult  hand 
these  extra  bones  become  ossified  with  the  proximal 
phalanx  of  the  corresponding  finger.  Another 
peculiarity  in  this  pedigree  is  the  abnormal^  great 
length  of  the  proximal  phalanx  of  the  ring  finger. 
All  these  anatomical  features  behave  as  a  unit  in 
inheritance,  with  remarkably  little  variation  in  their 
development  so  far  as  observed. 

Drinkwater  (191  7)  has  described  yet  another  digital 
abnormality,  which  is  remarkable  for  the  number  of 
generations  for  w^hich  it  is  known  to  have  been 
handed  down  in  one  family.  The  peculiarity  is  as 
follow^s,  as  found  in  the  hands  of  a  gentleman,  A.  T., 
of  the  present  generation :  In  the  middle  finger  the 
joint  between  the  middle  and  basal  phalanges  is  only 
very  slightly  movable,  the  articular  surfaces  of  the 
bones  being  enlarged,  while  in  the  ring  and  little 
fingers  there  is  no  joint  between  the  proximal  and 
middle  phalanges,  these  two  being  completely  fused 
into  one  (see  Fig.  17).  All  the  fingers  are  movable 
at  the  distal  joint,  and  both  hands  are  alike.  All  the 
toes,  except  the  hallux,  are  affected  exactly  like  the 
ring   and  little  fingers.     This   man's   father   and   his 


PHYSICAL  CHARACTERS  IN  MAX       87 

mother  are  known  to  have  had  precisely  the  same 
abnormality.  His  father  married  twice,  and  one  of 
the  half-brothers  shows  it.  The  most  interesting 
feature  of  this  case  is  that  A.  T.  is  a  direct  descendant 
in  the  male  line  from  John  Talbot,  the  first  Earl  of 
Shrewsbury,  who  figures  in  Shakespeare's  Henry  VI., 


Fig.  17. — Skiagram  (Photograph  by  Rontgen  Rays)  of  the 
Hands  of  A.  T.,  showing  Continuity  of  the  Proximal 
AND  Middle  Phalanges  in  the  Ring  and  Little  Fingers. 
(After  Drinkwater.) 


1 
:> 


and  was  killed  in  battle  near  Bordeaux  in  145 
Tradition  has  it  that  his  thigh  bone  was  broken 
while  on  horseback,  and  that  when  he  fell  from  his 
horse  he  was  killed  by  the  blow  of  a  battleaxe  on  the 
head.  His  body  was  buried  in  a  tomb  inside  the 
church  at  Whitchurch,  which  was  surmounted  by  a 


88  HEREDITY  AND  EUGENICS 

stone  effigy.  In  1874  the  tomb  was  opened  and  re- 
paired by  one  of  his  descendants.  The  skeleton  was 
identified  by  the  cleft  skull  and  the  fracture  of  the 
right  thigh  bone.  The  finger  bones,  when  examined, 
showed  the  same  ankylosis  that  exists  in  his  modern 
descendant.  On  the  stone  efhgy  the  fingers,  w^hich 
were  somewhat  damaged,  also  showed  precisely  the 
same  thickening  of  the  middle  joint  as  described  in 
his  descendant.  Clearly,  then,  this  defect  has  been 
handed  down  for  more  than  500  3^ears  as  a  Mendelian 
dominant,  and  the  genealogy  of  the  family  shows  that 
it  must  have  been  inherited  through  fourteen  genera- 
tions. This,  I  believe,  is  the  longest  period  on  record 
for  the  tracing  of  an  anatomical  abnormality  in  man, 
though  the  Hapsburg  jaw  extends  back  equally  far. 

In  America,  Cushing  (191 6)  has  described  essentially 
the  same  condition,  but  no  connection  with  the 
English  family  can  be  traced.  The  condition  in  this 
family  closely  resembles,  or  is  identical  wdth,  that 
in  Walker's  Maryland  family  (see  p.  84),  though  no 
relationship  between  them  has  been  traced  (see  also 
p.  82).  They  are  commonly  spoken  of  as  "  straight- 
fingered,"  because  the  fingers  can  only  be  partly 
closed  on  the  palm.  There  is  complete  absence  of  the 
proximal  joint  in  all  except  the  index  fingers,  in 
w^hich  there  is  a  trace  of  a  joint.  In  this  finger  slight 
movement  is  possible,  but  the  middle  phalanx  is  very 
short.  The  greater  effect  on  the  middle  phalanges  is 
true  also  of  Drinkwater's  minor-brachydactyly,  and 
is  probabty  due  to  the  fact  that  the  ossification 
centres  appear  later  in  this  phalangeal  row,  this  being 
the  last  row  to  ossify  and  the  terminal  row  the  first. 
The  toes  are  likewise  affected,  even  occasionally,  as 
in  ''  lobster  claw,"  when  the  hands  appear  normal. 
It  is  quite  probable,  according  to  Cushing,  that  the 
articulations  betw^een  the  proximal  and  middle  rows 
of  phalanges  are  the  last  to  be  laid  down,  and  that 


PHYSICAL  CHARACTERS  IX  jVIAN  89 

"  an  inhibitory  influence  checks  their  development 
at  a  stage  a  few  days  later  than  that  which  checks 
the  formation  of  the  ossification  centres  and  produces 
brach3^dactyly."  Hence  both  are  conditions  of 
arrested  development  in  different  degree. 

The  original  member  of  this  "  straight-fingered  " 
famil}^  Wilham  B.,  migrated  from  Scotland  to 
Virginia  in  1700.  He  married,  and  from  him  are 
descended  seven  generations,  most  of  whom  still  live 
in  the  same  region  of  Virginia.  A  member  of  the 
fifth  generation  has  communicated  with  a  Scottish 
relative  w^ho  shows  the  trait.  The  inheritance  is  that 
of  a  Mendelian  dominant,  the  family  including  452 
individuals  in  eight  generations.  Of  the  150  children 
of  an  affected  parent  in  twent3'-eight  completed 
families,  seventy-eight  of  them,  or  52  per  cent., 
carried  the  trait.  There  is  considerable  variation  in 
the  expression  of  the  character,  and  the  trait  ma}'  be 
transmitted  in  extreme  form  b}'  a  parent  who  appears 
to  be  but  slightly  affected.  In  one  case  a  woman  who 
was  doubtfull}'  abnormal,  but  transmitted  the  trait, 
was  shown  by  radiogram  to  have  the  condition  only 
on  the  little  finger  of  one  hand. 

Another  family  with  the  same  peculiarity  of  fingers, 
which  cannot  be  flexed  properly,  is  described  by 
Duncan  (191 7).  It  is  perhaps  related  to  Cushing's 
family,  since  its  ancestors  are  said  also  to  have  come 
from  Scotland.  The  second  joints  of  the  fingers, 
and  frequently  also  of  the  toes,  are  perfectly  inflexible. 
The  character  is  a  Mendelian  dominant  and  is  traced 
through  four  generations,  the  original  affected  parent 
(male)  being  apparently  heterozygous. 

Another  pedigree  of  a  short-fingered  family  is  given 
by  Mohr  and  Wriedt  (191 9),  who  review  the  literature 
of  brachydact3dy.  The  case  they  describe,  with 
numerous  photographs  and  radiographs,  is  of  a 
Norwegian  family,  some  of  whose  members  migrated 


90  HEREDITY  AND  EUGENICS 

to  North  America.  The  malformation  consists  in 
a  shortening  of  the  second  phalanx  of  the  second 
fingers  and  toes  only,  and  is  called  brachyphalangy. 
There  is  no  shortening  of  the  stature.  The  condition 
occurs  in  two  degrees:  (i)  so  slight  as  to  be  often 
overlooked  or  even  invisible;  (2)  more  extreme, 
probabh^  due  to  the  presence  of  a  modifying  or 
intensifying  factor.  The  inheritance  is  that  of  a 
simple  Mendelian  dominant.  It  has  been  traced 
through  five  generations  of  descendants  from  a 
brachyphalangous  woman  born  in  Norway  in  1 764. 
Detailed  knowledge  of  the  earlier  generations  is 
obtained  from  a  carefully  kept  "  family  book."  In 
two  lines  descended  from  an  affected  daughter  and 
an  affected  son  of  this  woman,  every  individual  is 
recorded.  In  one  case  intermarriage  within  affected 
lines  apparently  produced  an  individual  homoz3^gous 
for  the  character.  She  was  a  cripple  without  fingers 
or  toes,  and  died  at  the  age  of  one  year,  being  unable 
to  develop.  This  shows  how  serious  even  a  slight 
abnormality  ma}^  become  if  present  in  the  homoz3^gous 
condition.  It  corresponds  with  many  of  the  lethal 
factors  known  in  Drosophila.  The  writers  refer  to 
Mackinder's  (1857)  record  of  a  family,  in  which 
brachyphalangy  combined  with  h3^pophalangy  (less 
than  five  fingers)  was  transmitted  for  six  generations 
in  the  manner  typical  for  a  Mendelian  dominant 
character.  This  was  in  1857,  before  even  Mendel's 
original  work  was  done. 

Cragg  and  Drinkwater  (191 6)  describe  a  much  more 
extreme  case,  w^hich  Mohr  and  Wriedt  refer  to 
as  h\"pophalang3^  combined  with  brachyphalangy. 
There  is  an  entire  absence  of  the  distal  phalanges 
from  all  digits  except  the  thumb  and  big  toe,  and  an 
extremely  abortive  condition  of  the  middle  phalanx 
in  the  same  digits.  Nails  are  absent.  The  con- 
dition was  traced  as  a  Mendelian  dominant  through 


PHYSICAL  CHARACTERS  IX  .MAN         91 

five  generations,  including  twent^^-seven  affected 
individuals.  In  six  of  these  there  was  also  a  bifurca- 
tion of  the  thumbs,  which  may  be  due  to  the  presence 
of  a  dominant  modifying  factor.  Wegelin  ( 1 9 1  7)  traces 
through  three  generations  an  abnormalit}^  affecting 
only  the  little  fingers.  The  terminal  phalanx  is  bent  to 
the  radial  side,  the  middle  phalanx  shortened,  and  its 
distal  end  oblique.  It  is  dominant,  but  there  were  four- 
teen abnormal  to  two  normal  in  the  third  generation. 

The  remarkable  accuracy  of  the  inheritance  of 
many  digital  malformations  is  shown  incidentally  by 
a  paternity  case  (Mohr,  1921),  in  which  the  alleged 
father  had  a  pronounced  brachyphalangy  affecting 
the  second  row  of  phalanges  on  fingers  and  toes  II, 
III,  and  IV.  The  thumbs  were  normal,  but  the 
basal  phalanx  of  the  great  toe  was  shortened.  The 
hands  and  feet  of  the  child  showed  exactly  the  same 
malformation,  and  radiographs  indicated  absolute 
correspondence  in  the  bones.  The  man  was  there- 
fore adjudged  to  be  the  father. 

There  is  an  early  record*  of  a  peculiar  form  of 
brach3"dact\dy  in  which  the  mother  and  two  children, 
who  were  examined  at  Uxbridge,  had  normal  thumbs, 
but  the  fingers  had  only  one  phalanx  each,  except  the 
ring  finger  of  the  left  hand,  which  had  two  phalanges. 
There  w^ere  no  nails  on  these  fingers.  All  the  rest 
of  the  family  were  said  to  be  the  same,  and  the  con- 
dition was  stated  to  have  been  inherited  for  nine 
previous  generations,  but  there  are  no  records  to 
substantiate  these  statements.  The  character  was 
only  transmitted  by  the  w^omen,  who  sometimes  had 
a  child  wdth  perfect  fingers. 

In  another  case  (Rieder,    1899)   the   father   had   a 

rudimentary    (short)    fourth    metacarpal    bone,    the 

ring  finger  being  also  short  and  small.     The  daughter 

exhibited   "  lobster  claw  "   in   the  right   hand,   while 

*  Edin.  Med.  and  Surg.  Journ.,  1808,  iv.,  252. 


92  HEREDITY  AND  EUGENICS 

the  feet  showed  absence  of  certain  toes,  reduction  of 
certain  phalanges,  and  syndactyly.  Such  combined 
abnormalities  in  a  line  of  descent  are  not  infrequent. 
Stieve  (191 6)  describes  a  case  in  which  the  thumbs 
of  both  hands  have  an  extra  joint.  He  cites  39  cases 
from  the  literature  in  which  there  is  a  supernumerary 
phalanx  on  both  thumbs,  and  16  in  which  it  is  on 
only  one.  In  33  cases  of  the  former  condition, 
occurring  in  10  different  families,  the  condition  is 
known  to  be  inherited,  while  there  is  no  evidence  of 
its  inheritance  when  it  occurs  on  only  one  hand. 

Danforth  (igiga)  describes  a  condition  which  he 
calls  brachydactyly  in  fowls.  Such  birds  differ 
from  the  normal  in  that  digit  IV,  instead  of  having 
five  phalanges  and  being  longer  than  digit  II, 
varies  from  as  long  as  II  (not  longer)  to  a  toe 
having  only  two  phalanges  and  no  nail.  He  treated 
with  alcohol  {igigb)  fowls  which  w^ere  heterozygous 
for  brachydactyly,  Polydactyly  (extra  toes),  and 
white  colour — both  males  and  females,  the  alcohol 
being  inhaled  for  short  periods.  A  larger  percentage 
of  brachydactylous  birds  was  consistently  obtained 
in  the  offspring  of  treated  males,  indicating  that 
germ  cells  carrying  brachydactyly  were  more  re- 
sistant than  normal  germ  cells,  or  possibly  (though  this 
seems  unlikely)  that  alcohol  damaged  the  sperma- 
tozoa so  as  to  produce  the  defect.  This  experimental 
method  should  be  applicable  to  a  variety  of  cases, 
and  furnish  evidence  of  the  relative  viability  of 
different  types  of  germinal  differences.  Ultimately 
it  might  lead  to  a  method  of  selectively  eliminating 
certain  undesirable  types  of  germ  cells.  The  studies 
of  Pearl  on  the  eifects  of  alcohol  on  pure  races  of 
fowls,  of  Harrison  with  moths,  and  some  other  similar 
results,  indicate  that  in  such  cases  there  is  a  selective 
weeding  out  of  weaker  germ  cells,  leaving  the  stronger 
to  take  part  in  development. 


PHYSICAL  CHARACTERS  IX  :\rA\         93 

Polydactyly  and  syndactyly  (fingers  or  toes  united 
by  a  web  of  flesh)  are  also  well  known  as  inherited 
conditions.  Thus  Reaumur's  case  of  a  Maltese  couple 
having  a  hexadactylous  son,  three  of  whose  children 
were  again  hexadactylous,  is  referred  to  by  Huxley 
{Darwiniana,  p.  35).  But  usually  such  pedigrees  are 
incomplete,  no  account  being  taken  of  the  normal 
members  of  the  family.  Windle  (1891)  cites  an 
instance  from  Clement  Lucas,  where  six  fingers  or 
toes  were  inherited  in  a  family  through  four  genera- 
tions. There  appear  to  have  been  twenty-five 
normals  to  seventeen  hexadact^ds.  In  other  records 
the  condition  has  been  followed  for  six  and  five 
generations  respectively.  There  is  some  evidence  that 
Polydactyly  is  more  common  in  negroes  than  in  whites. 

Lewis  (1909^?)  describes  Lucas's  case,  in  which 
in  several  related  families  in  two  generations  there 
are  twenty-four  normals  to  fifteen  polydactyls. 
Other  records  cited  show  that  the  abnormality  may 
skip  a  generation.  There  is  a  large  degree  of  variation 
in  the  extent  to  which  this  dominant  character  is 
developed.  Polydactylism  is  found  not  only  in  man, 
horses,  fowls,  and  guinea-pigs,  but  also  in  monkeys, 
dogs,  cats,  and  other  animals.  Bonavia  (1895)  gives 
several  pedigrees  of  hexadact3dy  in  man,  with  a  good 
many  cases  of  the  inheritance  of  various  abnormalities 
and  sudden  monstrous  variations  in  a  number  of 
different  animals. 

Albert  (191 5)  describes  a  family  with  thirteen  cases 
of  fused  or  webbed  fingers  or  toes  traced  through  finir 
generations.  The  condition  w^as  obviously  hereditary, 
but  was  not  inherited  as  a  regular  dominant  or  re- 
cessive character.  In  three  cases  it  appeared  in 
children  neither  of  whose  parents  were  affected,  when 
at  least  one  of  the  parents  had  also  a  normal  family 
history.  Probably  such  irregularities  in  the  ex- 
pression of  a  character  result  from  inhibition  of  its 


94  HEREDITY  AND  EUGENICS 

development  by  the  presence  of  other  determiners. 
Many  instances  of  the  influence  of  hereditary  de- 
terminers upon  each  other  are  now  known  from 
experimental  breeding. 

Schofield  (1922)  describes  a  case  of  webbed  toes 
which  occurs  in  fourteen  male  members  of  a  family 
in  four  generations.  The  web  appears  only  between 
the  two  toes  next  the  great  toe,  and  is  confined  to  the 
skin  and  flesh.  It  is  always  more  marked  in  the 
right  foot  than  the  left,  and  is  confined  to  the  males, 
being  transmitted  only  from  father  to  son.  It  thus 
follows  the  course  of  the  Y-chromosome.  The  only 
case  of  this  type  of  inheritance  which  has  been 
experimentally  investigated  (Schmidt,  1920)  occurs 
in  the  "  millions  "  fish,  Lebistes  reticulatus,  which  is 
a  native  of  the  West  Indies.  A  dark  spot  on  the 
dorsal  fin  in  certain  males  is  transmitted  in  crosses 
to  all  the  male  offspring,  but  is  not  transmitted 
through  the  female  line  at  all.  Castle  (1922)  has  also 
recently  pointed  out  the  significance  of  this  type  of 
inheritance  in  man. 

Polydactyly  and  syndactyly  in  various  forms  are 
not  infrequently  found  together.  A  case  of  the  kind 
has  been  described  in  cats  (Howe,  1902).  A  strain  of 
polydactylous  cats  in  Cambridge,  Massachusetts,  was 
descended  from  a  polydactyl  cat  at  the  Harvard 
Astronomical  Observatory.  One  of  these  cats  was 
dissected,  having  six  toes  on  each  fore  paw,  and  the 
toes  of  the  hind  paws  fused  in  pairs  almost  to  the  ends 
of  the  claws. 

Castle  (1906)  has  described  the  origin  of  a  poly- 
dactylous race  of  guinea-pigs.  He  sa3^s  that  in  man 
"  polydactylism  usually  makes  its  (recorded)  ap- 
pearance in  some  noteworthy  form,  is  transmitted 
more  or  less  strongly  through  tw^o  to  five  generations, 
and  then  disappears,  doubtless  so  weakened  by  re- 
peated outcrosses  that  its  manifestations,  if  any  occur, 


PHYSICAL  CHARACTERS  IN  MAN         95 

are  no  longer  observed."  Normal  guinea-pigs  have 
four  toes  on  each  front  foot,  but  only  three  on  each 
hind  foot.  Castle's  polydactylous  race  had  four  on 
all  feet.  The  missing  digits  in  normals  are  the  thumb 
from  the  fore  feet,  and  I  and  V  from  the  hind  feet. 
The  polydact\dous  race  was  established  from  one  rare 
individual  (mutation),  and  was  afterwards  found 
twice  in  breeders'  animals,  but  was  not  hitherto 
known  in  any  wild  or  domesticated  Caviidce.  By 
selection  through  five  generations  a  polydactylous 
race  was  gradually  established  in  which  all  the 
offspring  were  polydactylous.  The  inheritance  is 
neither  Mendelian  nor  blending,  but  probably  inter- 
mediate between  the  two.  Without  the  aid  of 
selection,  polydactylism  would  probabl}^  never  become 
a  racial  character. 

In  poultry,  Bateson,  Davenport,  and  others  have 
shown  that  the  extra  toe,  which  has  for  a  long  time 
been  an  established  character  in  some  breeds,  is  not 
strictly  Mendelian  in  its  inheritance,  although  it  is 
more  strongly  established  than  in  the  four-toed  race 
of  guinea-pigs. 

Radiograms  of  a  hexadactylous  Italian  immigrant 
with  six  fingers  and  toes  are  given  in  Joiirn.  Heredity, 
vii.,  320  (1916).  The  condition  appears  to  be  due  to 
a  split  in  the  rudiment  of  the  fifth  finger.  A  five- 
toed  pigeon,  due  to  a  similar  split  in  the  rudiment  of 
one  toe,  is  also  shown.  A  case  in  which  the  thumb 
is  more  or  less  completely  missing  from  both  hands 
is  photographed  in  Journ.  Heredity,  vii.,  224  (191 6). 
There  were  various  digital  malformations  in  the 
relatives. 

Bond  (1920)  crossed  various  five-toed  and  four- 
toed  breeds  of  fowls.  The  former  were  the  silky 
Dorking  and  Faverolle,  and  the  latter  Old  English 
Game,  Wyandotte,  and  Orpington.  The  proportions 
of  four-toed  to  five-toed  and  heterodactylous   birds 


96  HEREDITY  AND  EUGENICS 

(with  four  toes  on  one  foot  and  five  on  the  other) 
varied  somewhat  according  to  whether  the  male  or 
female  belonged  to  the  five-toed  breed,  and  also  in 
Fj  as  compared  with  F^.  In  a  total  of  402  birds,  172 
had  four  toes  on  both  feet ,  and  3  8  were  heterodact^dous . 
Of  the  latter,  34  had  the  extra  digit  on  the  left  side 
and  only  4  on  the  right.  In  2  birds  rudiments  of 
six  toes  appeared,  suggesting  that  the  character  for 
extra  toe  is  not  stable.  Bateson  and  Punnett  also 
found  that  among  89  asymmetric  birds  from  various 
matings,  the  extra  digit  was  on  the  left  side  in  y2 
cases,  and  on  the  right  in  17.  In  49  other  birds  the 
extra  toe  was  larger  on  one  side  than  on  the  other, 
being  larger  on  the  left  side  in  34  of  these  cases,  and 
smaller  in  15.  Barfurth,  in  similar  matings  between 
normal  and  h^^perdact^dous  fowls,  obtained  556 
four-toed  and  475  hyperdact3dous.  Of  the  latter, 
6s  were  asymmetrical,  35  having  the  extra  toe  on 
the  left  and  30  on  the  right.  In  another  list  12  birds 
were  left-sided  and  6  right-sided.  Castle  (1906) 
in  guinea-pigs  also  found  a  slight  tendency  for 
the  extra  toe  to  appear  on  the  left  side.  Out  of 
1,219  individuals,  630  had  the  extra  digit  on  the 
left  and  582  on  the  right.  The  explanation  is  not 
clear. 

Bonnevie  (191 9)  describes  a  type  of  postaxial 
Polydactyly  in  man,  which  is  usualty  stronger  on  the 
right  side  of  the  body.  The  extra  finger  arises  from 
the  base  of  the  little  finger,  the  metacarpal  bones  being 
normal.  There  is  much  variation  in  this  abnormality, 
and  families  showing  it  are  now  distributed  all  over 
Norway,  but  they  are  all  probably  descended  from 
the  same  ancestor  about  300  3^ears  ago.  Boas  (191 7) 
assigns  two  causes  for  polydact3dy  in  horses : 
(i)  Atavism,  "  Hipparion-toes  ";  (2)  doubling  of 
certain  digital  parts  of  the  foot.  The  case  of  Caesar's 
horse,  which  belonged  to  the  former   class,  is  well 


PHYSICAL  CHARACTERS  IN  MAN         97 

known.*  This  condition  is  rare.  More  or  less  complete 
doubling  of  the  extremities  occurs  in  various  mammals. 
Cramer  (1910)  discusses  cases  of  pol3^dactyly  in  man, 
horses,  a  lamb,  fowls,  pigs,  and  a  calf.  Fackenheim 
(1888)  describes  a  family  in  which  hereditary  Poly- 
dactyly is  combined  with  tooth  anomalies.  The  Heizler 
family  show^ed  Polydactyly  as  a  simple  dominant  in 
four  generations.  A  polydactylous  man  of  the  third 
generation  married  a  woman  with  tooth  anomalies, 
having  two  abnormally  large,  pointed  teeth  in  place 
of  the  incisors  and  only  two  cheek  teeth.  Of  their 
six  children,  three  were  normal  and  three  showed 
both  abnormalities  with  some  variations  in  the  con- 
dition of  the  teeth. 

A  recent  case  of  polydactylism  in  cattle  is  described 
(Roberts,  1921).  Many  instances  have  been  recorded. 
In  this  one,  from  a  herd  of  dairy  cattle  in  Illinois,  a 
normal  bull  mated  with  a  polydactylous  cow,  having 
three  toes  on  each  foot,  produced  a  polydactN'lous 
female.  She  was  mated  to  a  normal  unrelated  bull 
and  produced  three  male  calves,  all  polydactylous, 
but  one  with  a  duplication  of  the  metatarsal  bones 
of  the  hind  feet,  which  bore  four  and  five  toes  re- 
spectively. The  character  is  evidently'  dominant  in 
inheritance.  The  third  or  extra  toe  is  on  the  inside, 
and  probably  represents  digit  II.  It  is  alwa3^s 
larger  on  the  hind  feet  than  on  the  fore  feet. 

Bateson  (1894,  p.  376)  describes  a  three-toed  strain 
of  cattle  from  a  three-tged  cow  bought  in  1 861 .  The 
strain  lasted  until  1887,  producing  about  ten  genera- 

*  The  reference  is  in  Suetonius,  Bk.  I.,  chap.  Ixi. :  "  Utebatur 
autem  equo  insigni,  pedibus  prope  humanis  et  in  inoduin  digi- 
torum  unguUs  fissis."  ("He  rode  a  remarkable  horse  too,  with 
feet  that  were  almost  human,  for  its  hoofs  were  cloven  in  such  a 
way  as  to  look  like  toes.")  The  writer  goes  on  to  say  that  it  was 
born  in  Caesar's  stables,  that  he  tended  it  with  great  care  and  was 
the  first  to  mount  it,  and  that  a  statue  of  it  was  afterwards  dedi- 
cated in  front  of  the  temple  of  Venus  Genetrix. 

7 


98  HEREDITY  AND  EUGENICS 

tions.  The  condition  appeared  in  both  males  and 
females,  but  the  bulls  were  not  kept,  so  transmission 
was  only  through  the  cows.  About  two  calves  in  three 
had  the  extra  toe.  The  abnormality  was  confined 
to  the  hind  feet,  except  in  one  case.  As  the  last 
members  of  the  strain  were  all  males  the  breed  was 
lost.  This  instance  of  Polydactyly  is  very  similar 
to  the  last.  The  inheritance  was  evidently  the  same, 
but  the  character  itself  show^s  the  interestinsr  difference 
that  it  is  less  extreme.  It  is  confined  to  the  hind  feet, 
except  in  one  individual,  whereas  in  Roberts's  herd 
it  is  present  on  all  four  feet,  but  is  larger  on  the  hind 
feet.  Such  slight  constant  differences  in  abnormali- 
ties are  of  fairly  frequent  occurrence,  and  they  throw 
an  interesting  sidelight  on  the  structure  of  the  germ 
plasm  and  the  almost  infinite  variety  of  the  changes 
which  it  can  undergo. 

A  very  good  case  of  syndactyly  in  ungulates  is 
that  of  the  mule-foot  hog,  a  type  with  solid  instead  of 
cloven  hoofs,  which  has  long  been  known  in  the 
Western  States  of  America,  and  is  also  found  in 
Germany  and  elsewhere.  Detlefsen  and  Carmichael 
(1921)  find  that  in  crosses  between  a  pure-bred  mule- 
foot  boar  and  pure-bred  Duroc-Jersey  sows  the 
offspring,  numbering  about  250,  were  all  black  and 
mule-footed  like  the  sire.  Later  generations  showed 
that  syndactyly  was  a  simple  dominant  to  normal, 
and  black  to  red  of  various  shades. 

Bateson  (p.  387)  gives  numerous  data  on  the  subject. 
He  states  that  solid  hoofs  in  pigs  is  a  relatively  common 
variation,  that  they  are  mentioned  by  Aristotle, 
and  are  found  in  various  parts  of  the  world.  Sir 
N.  Menzies  at  Rannock,  Scotland,  had  a  breed  of  such 
hogs  for  forty  years.  They  came  from  a  pair,  and 
were  black  and  of  smaller  size  than  the  type,  with 
smaller  ears.  Their  flesh  was  considered  more  sweet 
and  tender,  and  several  hundred  were  bred  at  a  time. 


PHYSICAL  CHARACTERS  IN  MAN  99 

In  crosses  they  sliowed  alternative  inheritance,  but 
they  tinally  became  extinct.  Another  pair  of  solid- 
hoofed  pigs  was  received  by  the  Zoological  vSociety 
of  London  from  Cuba  in  1876.  Auld  (1889)  reports 
sohped  (solid-hoofed)  swine  from  Texas  in  1878.  They 
bred  true,  and  when  crossed  with  the  normal  gave  a 
majority  of  solipeds.  Another  breed  of  solid-hoofed 
hogs  was  reported  from  a  farm  at  Sioux  City,  Iowa, 
and  a  wild  herd  from  near  Baton  Rouge,  Louisiana. 
In  another  instance  a  Poland-China  boar  with  one 
solid  hoof  had  many  offspring  in  the  same  condition. 
Probably  the  solid-hoofed  condition  has  arisen  many 
times  through  independent  mutations. 

A  peculiar  case  is  recorded  by  Colonel  Hallam*  of 
a  race  of  pigs  observed  in  a  town  on  the  coast  of  the 
Tanjore  countr}'  in  1795.  Drawings  of  two  in- 
dividuals were  submitted.  The  pigs  had  only  two 
legs,  the  hinder  extremities  being  entirely  wanting. 
They  bred  true  for  at  least  three  generations.  Such 
cases  must  arise  through  some  mishap  to  an  element 
of  the  germ  plasm. 

Darwinf  cites  the  following  conditions  in  horses 
as  plainly  hereditary:  ring-bones,  curbs,  splints, 
spavins,  founder  and  weakness  of  the  front  legs, 
roaring  or  broken  and  thick  wind,  melanosis,  specific 
ophthalmia,  blindness,  crib-biting,  jibbing,  and  ill- 
temper.  He  quotes  Youatt :  "  There  is  scarcely  a 
malady  to  which  the  horse  is  subject  which  is  not 
hereditary." 

Many  records  of  syndactyly  in  man  are  extant, 
but  usually  the  inheritance  has  only  been  traced  from 
parent  to  offspring.  It  is  recognised  as  a  Mendelian 
dominant  condition.  Hurlin  (1921)  describes  a  case 
of  limited  syndactyl}^  in  an  old  New  England  family 
in  which  the  web  occurs  only  between  the  second  and 

*  Proc.  Zool.  Soc,  1833,  Part  I.,  p.  t6. 
t  Animals  and  Plants,  chap,  xii.,  p.  -45^. 


loo  HEREDITY  AND  EUGENICS 

third  toes,  and  is  sometimes  even  there  so  slight  as 
to  be  scarcely  noticeable.  It  is  not  found  in  the 
hands  at  all.  The  condition  is  found  in  the  grand- 
father, in  his  onl}^  child  (a  son),  and  in  three  out  of 
six  of  the  F2  generation  in  accordance  with  Mendelian 
expectation.  There  is  no  doubt  that  innumerable 
slight  abnormalities  of  this  kind  occur  in  man  and 
are  inherited  in  the  Mendelian  manner,  as  has  been 
shown  to  be  the  case  with  many  similar  mutations 
in  Drosophila. 

Schultz  (1922)  adopts  Weidenreich's  term  zygo- 
dactyly for  true  webbing,  confining  the  term  syn- 
dactyly to  those  cases  where  a  union  or  fusion  of 
bones  is  involved.  Zygodactyly  is  found  in  many 
mammals.  In  a  Sumatran  ape  Siamanga  syndactyla 
(see  Wallace,  Malay  Archipelago,  p.  134),  the  two  first 
digits  of  the  feet  are  joined  together  nearly  to  the 
end.  In  an  early  stage  of  development  of  the  human 
foot  the  toes  are  all  webbed,  and  the  webbing  extends 
slightly  further  between  the  second  and  third  toes 
than  between  any  others.  Webbing  or  zygodactyly 
is,  therefore,  a  case  of  arrested  development.  It  is 
also  found  that  when  certain  toes  are  webbed  the 
corresponding  tendons  are  joined  for  a  greater  dis- 
tance. Schultz  cites  the  observations  of  Schurmeier, 
who  examined  20,000  men  in  the  American  army 
and  found  8  cases  of  zygodactyly,  always  between 
toes  II  and  III.  This  condition  was  combined 
in  some  cases  with  webbing  of  fingers  III  and  IV, 
or  I  and  II  and  III  and  IV,  or  all  fingers.  In  a 
family  described  by  Sommer,  the  webbing  of  toes 
II  and  III  was  only  on  the  right  foot  in  all  members, 
the  pedigree  extending  through  five  generations. 
It  was  inherited  by  both  sexes,  probably  as  a  simple 
dominant.  In  Schofield's  (1922)  family  the  webbing 
is  always  longer  on  the  right  foot  and  is  transmitted 
only  from  male  to  male,   appearing  in  all  the  sons 


PHYSICAL  CHARACTERS  IN  MAN        loi 

(13  cases)  and  none  of  the  daughters  (it  cases)  and 
following  the  Y  chromosome.  In  Hurlin's  family, 
mentioned  above,  the  webbing  was  longer  on  the 
left  foot  and  was  exhibited  in  both  sexes.  In  three 
other  families,  by  Pfitzner,  Wolff,  and  Wile,  the 
character  also  appears  to  be  a  simple  dominant. 

Sometimes  syndactyly  and  polydactyl}^  appear  in 
the  same  family,  as  in  the  family  described  by 
Manson  (191 5).  This  family  originated  from  one 
William  Joseph,  born  in  Aberystwyth  about  the 
beginning  of  the  nineteenth  centur3^  He  had  webbing 
of  the  third  and  fourth  fingers  of  his  hands,  and  six 
toes  on  each  foot,  and  was  probably  homozygous  for 
this  condition,  since  his  nine  children  all  had  it. 
They  married  normals,  and  had  a  total  of  eighteen 
children  affected,  eighteen  normal,  four  doubtful. 
In  only  three  descendants  is  the  abnormality  com- 
plete in  all  four  limbs.  One,  two,  or  three  limbs  may 
escape.  Skiagraphs  show  incomplete  polydact^dism 
in  some  cases.  There  is  considerable  variation  in  the 
condition,  but  skiagraphs  show  clearly  that  the  fourth 
digit  of  the  hands  and  feet  is  consistenth^  affected 
by  complete  or  partial  reduplication.  Another  poly- 
dactylous  family  is  described  by  Atwood  and   Pond 

(1917)-  .  _ 

Many  data  concerning  hyperdact}^}'  are  given  in 

a    paper    by    Ballowitz    (1904).      Records    of    extra 

fingers  and  toes  are  known  not  only  in  "  Caucasians," 

but  also  in  Negroes,  Arabs,  Chinese,  and  Amerindians 

(North  American  Indians).     Most  frequenth^  only  an 

extra  terminal  phalanx  is  present,    but    six-fingered 

men  have  been  known   from  the   earliest   times.     In 

the  Bible  (2  Sam.  xxi.  20)  a  "  giant  "  is   mentioned 

who  had  six  fingers  on  each  hand  and  six  toes  on 

each  foot.      He  was  one  of  four  men  of  exceptional 

stature — sons    of    a   giant.     Pliny   referred   to   hexa- 

dactylous    persons    as    Sedigiti.      Anne    Boleyn,    the 


I02  HEREDITY  AND  EUGENICS 

beautifulwifeof  Henry  VIII.,is  said  to  have  had  super- 
numerary breasts,*  teeth  anomalies,  and  an  extra 
terminal  phalanx  on  hands  and  feet.f  The  "  outside  " 
digits — i.e.,  thumb  and  little  finger  and  great  and 
little  toe — most  commonly  show  doubling.  Doubling 
of  other  digits  is  much  more  uncommon,  becoming 
still  more  so  as  the  number  increases.  Thus  the 
presence  of  ten  digits  on  one  hand  or  foot  is  extremely 
uncommon  in  museums,  while  cases  of  seven  are 
relatively  often  described.  This  condition  is  often 
combined  with  other  abnormalities,  but  hexadactyly 
and  heptadactyly  often  occur  in  otherwise  normal 
individuals.  The  extra  digits  are  frequently  syn- 
dactylous,  not  fully  separated  from  their  neighbours. 
Hexadactyty  is  often  symmetrical  (two  double 
thumbs  or  two  double  little  fingers),  but  there 
are  man}^  exceptions,  and  scarcely  two  cases  agree 
in  detail. 

Three  main  types  of  abnormality  appear : 
(i)  Simplest  and  most  common;  the  extra  digit  is  a 
small  attachment  not  adherent  to  the  skeleton,  and 
often  without  bones  or  cartilage,  muscle  or  tendons. 
(2)  Often  the  extra  digit  is  more  or  less  like  an 
ordinary  finger  or  toe,  containing  bones  and  con- 
nected with  the  skeleton  of  the  finger.  (3)  Ver}^ 
seldom  the  extra  digit    is  complete  and  also  has  its 

*  Other  cases  of  supernumerary  mammae  in  more  than  one 
generation  are  cited,  for  example,  by  Darwin,  Descent  of  Man, 
p.  41. 

t  The  only  confirmation  of  this  statement  I  have  been  able  to 
find  is  the  following,  from  Wyat's  Life  of  Anne  Boleyn  (Ed.  Singer, 
p.  423) :  "  There  was  found,  indeed,  upon  the  side  of  her  nail 
upon  one  of  her  fingers  some  little  show  of  a  nail,  which  yet  was 
so  small,  by  the  report  of  those  that  have  seen  her,  as  the  work- 
master  seemed  to  leave  it  an  occasion  of  greater  grace  to  her  hand, 
which,  with  the  tip  of  one  of  her  other  fingers,  might  be,  and  usually 
was,  by  her  hidden,  without  any  least  blemish  to  it."  It  is  a  fact, 
however,  that  among  the  portraits  of  the  wives  of  Henry  VIII., 
Anne  Boleyn's  is  the  only  one  in  which  the  hands  are  not  shown. 


PHYSICAL  CHARACTERS  IN  MAN        103 

own    metacarpal    or   metatarsal    bone.     All    possible 
intergrades  are  said  to  occur  between  these  forms. 

Russian  statistics  are  quoted  of  fourteen  families 
in  w^hich  the  extra  finger  is  inherited,  also  ten  families 
with  six  fingers  and  six  toes,  while  Hennig  in  1880 
recorded  Polydactyly  in  sevent3^-seven  families.  The 
condition  may  extend  through  two  to  five  or  many 
generations,  and  ten  to  forty  h3^perdactylous  in- 
dividuals have  been  recorded  in  many  families. 
Polydactylous  twins  are  twice  recorded,  and  one 
polydactylous  twin  sister  had  four  normal  sisters. 
Reaumur's  Maltese  family  is  also  quoted  in  detail 
by  Ballowitz.  In  two  generations  descended  from 
Gratio  Kaleia,  who  had  six  fingers  on  each  hand  and 
six  toes  on  each  foot,  and  his  normal  wife,  there  were 
ten  hexadactyls  and  six  normals,  but  in  the  former 
the  abnormality  did  not  always  appear  on  all  four 
limbs.  In  the  pedigree  of  Elizabeth  Horstmann  of 
Rostock  (Mecklenburg),  who  had  six  digits  on  all 
four  limbs,  her  daughter  was  like  the  mother,  and 
the  next  two  generations  from  marriages  with  normals 
gave  seven  hexadactyl  to  seven  normal,  in  conformity 
with  expectation  for  a  simple  Mendelian  dominant. 
In  another  pedigree,  Marie  Schweizer  of  Fischbach, 
three  generations  of  descendants  include  eight  hexa- 
dactyl and  ten  normal.  In  yet  another  hexadactylous 
pedigree  (Alexander)  there  were  in  three  generations 
of  descendants  nine  hexadactyls  to  ten  normals.  All 
hexadactylous  individuals  in  this  pedigree  showed 
a  striking  symmetr}^  and  in  one  male  the  condition 
was  combined  with  S3'ndactyly.  In  another  pedigree, 
quoted  from  Marchand,  in  which  the  condition  ran 
through  five  generations,  a  family  of  eight  in  the 
fourth  generation  all  had  six  fingers  and  six  toes. 
The  father,  who  was  hexadactylous,  must  have 
been  homozygous  for  the  trait.  The  family  of  the 
Sultan  of  Pontianak  (Borneo)  is  hexadactylous,  and 


I04 


HEREDITY  AND  EUGENICS 


this  condition  is  recognised  in  each  generation  as  a 
mark  of  ro^^al  distinction  !  Ballowitz  quotes  from 
the  French  hterature  (1863)  the  case  of  an  isolated 
village  in  the  Departement  d'Isere,  in  which,  through 
inbreeding,  nearly  all  the  inhabitants  had  six  fingers 
and  toes.  Later,  owing  to  increased  communications, 
marriages  with  normals  took  place,  and  the  extra 
fingers  and  toes  in  newborn  children  became  smaller 
and  fewer,  finally  disappearing  altogether.  This  is 
a  good  example  of  the  "  weakening  "  and  disappear- 
ance of  an  abnormality  through  exogamy,  but  brachy- 
dactyly  does  not  appear  to  be  affected  in  this  way. 


D  X 


6-6 
^6-6 


°      □  X   ^5 


1 1         I         I         I         I 


6-6 


10  Other  children,  all  having  6  Fingers  and  toes. 


m    il«,    X     o 


66 


65 
6-5 


1 6-6 
\6-6 


i6-6 


w 


iff  6     i 


6-6 
6-6 


i66 

I  6-6 


V — 

Twins 


^6-6 

mee 

Zerah 


^^ 


Fig.  i8. — Pedigree  of  Hexadactyly. 


If  such  weakening  of  a  character  like  hexadactyly 
can  take  place  through  exogamy,  it  is  an  important 
hereditary  principle  which  requires  further  elucida- 
tion, especial^  in  comparison  with  conditions  like 
brachydactyly  where  no  weakening  effect  is  observed 
even  after  many  generations  of  outcrossing. 

An  interesting  hexadactylous  family  is  described 
by  Carlisle  (1814).  Zerah  Colburn,  the  son  of  Abiah 
Colburn,  born  in  \^ermont,  was  brought  to  London 
on  account  of  his  "  extraordinary  powers  in  arith- 
metical computations  from  memory."  He  had  a 
supernumerary   little  finger   on   each    hand,   and   an 


PHYSICAL  CHARACTERS  IN  MAN        105 

extra  little  toe  on  each  foot.  The  extra  digits  were 
all  perfectly  formed,  with  nails  and  three  phalanges. 
The  father  also  was  hexadactylous,  having  five 
metacarpal  bones,  but  six  metatarsals.  The  pedigree 
of  this  family  through  four  generations  is  given  in 
Fig.  18.  Beside  each  is  given  (above)  the  number 
of  fingers  and  (below)  the  number  of  toes.  The  in- 
heritance is  strictly  that  of  a  Mendelian  dominant, 
with  occasional  failure  of  one  hand  or  foot  to  exhibit 
the  abnormality. 

In  another  hexadactylous  famil}^  (Sedgwick,  1863, 
p.  188)  an  extra  finger  with  two  phalanges  and  a  nail 


f 


xO 


o^ 


'xn 


ixo 


i 


i 


6.6 

6.6 


I 


6.5 


W~^^ 


66  66 


Fig.   19. — Hexadactylous  Family. 

was  attached  to  the  base  of  the  first  phalanx  of  each 
little  finger.  The  condition  was  followed  through 
four  generations.  There  was  some  variation  in  its 
expression,  and  it  skipped  two  generations  both  in 
the  male  and  the  female  line  (see  Fig.  19). 

Schroeder  (191 8)  described  a  condition  of  hypo- 
dactyly  appearing  in  the  hands  and  feet  of  a  family 
for  five  generations  and  accompanied  by  other 
deformities.  The  strain  originated  with  a  woman, 
who  is  said  to  have  had  normal  parents.  She  j^ro- 
duced  three  affected  and  two  normal  children,  the 
latter   having   only   normal   .descendants,    while    the 


io6  HEREDITY  AND  EUGENICS 

former  had  twenty-eight  normals  to  sixteen  affected 
offspring.  The  condition  is  transmitted  by  both 
sexes,  and  shows  a  tendency  to  become  less  marked 
in  later  generations. 

Hawkes  (191 4)  has  compared  different  t^^pes  of 
human  foot  as  regards  the  relative  lengths  of  the 
first  and  second  digits.  From  an  examination  of  the 
feet  of  2,300  persons,  chiefly  children,  he  finds  the 
"  L  "  type  of  foot,  with  the  great  toe  longest  and 
the  other  toes  sloping  back  in  an  oblique  line,  the 
commonest.  The  ''  S  "  type,  in  which  the  second 
toe  is  longer  than  the  great  toe,  is  much  less  common. 
Not  very  rarely  one  foot  will  be  of  the  L  type,  and 
one  of  the  S  type.  This  is  in  hetero zygotes,  but 
some  persons  with  both  feet  L  are  heteroz3^gous.  The 
"  E  "  type,  in  which  digits  I  and  II  are  of  equal 
length,  is  very  unusual.  The  L  t3^pe  of  foot  shows 
irregular  dominance  over  the  S  t3^pe  in  inheritance, 
but  the  S  type  occurs  more  commonty  in  females  than 
in  males,  and  is  commonest  in  the  foetal  stage.  The 
male  heteroz}^gote  tends  to  be  L,  and  the  female  to 
be  S,  in  foot  pattern.  Occasionalh^  digit  III  is 
longer  than  digit  II,  and  this  condition  is  also  found 
to  be  hereditar}^ 

Various  Abnormalities. 

Lundborg  (1920)  concludes  that  hereditary  deaf- 
mutism  is  due  to  one  Mendelian  recessive  factor,  and 
rejects  Plate's  h^^pothesis  of  two  factors.  Acquired 
deaf-mutism  ma\^  be  either  intra-  or  extra-uterine 
in  origin.  Hence  congenital  deafness  is  not  always 
hereditar\^.  Irish  statistics  of  the  ^xar  1891  register 
congenital  deaf-mutism  as  "jG  per  cent,  of  all  cases. 
In  Norwa^^  (1897)  the  number  was  estimated  at  50-9 
per  cent.,  in  Sweden  (1904)  at  40-8  per  cent.,  and  in 
the  Malmohus  district  of  Sweden  (191 9)  at  only 
28-2  per  cent.  (108  in  383).     Meningitis  and  scarlatina 


PHYSICAL  CHARACTERS  IN  MAN        107 

are  said  to  be  the  most  common  causes  of  acquired 
deaf-mutism.  In  addition  to  the  difhcuh}^  in  dis- 
tinguishing between  genotypical  (inherited)  and 
phenotypical  (acquired)  deaf-mutism  a  statistical  error 
is  introduced  by  the  fact  that  in  small  families  the 
children  may  all  be  normals,  even  when  the  parents 
are  heterozygous  for  the  condition.  Since  these 
children  are  not  added  to  the  offspring  of  matings  of 
heterozygotes,  the  result  is  more  than  25  per  cent,  of 
abnormals.  This  can  be  corrected  by  applying  a 
formula  of  Weinberg,  and  it  then  closely  approxi- 
mates to  the  expected  25  per  cent. 

From  Fay's  evidence  of  marriages  of  the  deaf  in 
America  (1898),  twenty-two  families  had  four  to 
nine  children  each,  all  deaf.  The  children  numbered 
112.  Hence  it  appears  that  genotypical  deaf-mutes 
will  have  only  deaf-mute  children,  and  from  this  and 
other  evidence  it  appears  that  the  character  is  prob- 
ably a  simple  recessive.  The  difficulty  in  all  statistics 
on  this  subject  is  to  distinguish  between  genotypic 
and  phenotypic  deaf-mutism.  Love  (1920)  also 
reaches  the  conclusion  that  sporadic  congenital 
deafness  is  inherited  as  a  Mendelian  recessive,  from 
a  stud}^  of  an  Ayrshire  famil}^  which  has  branches  in 
America  and  Australia.  This  famil}'  shows  five 
affected  generations  descended  from  a  common 
ancestor  three  generations  further  back.  Yearsle}' 
(1920)  gives  an  account  of  a  family  with  a  history  of 
''  acquired  "  deafness,  which  produced  offspring  born 
deaf.  But  as  the  acquired  deafness  is  apparentl}' 
hereditary  otosclerosis,  this  is  merely  a  case  of  the 
earlier  appearance  of  the  abnormality.  Home  (1909), 
in  a  study  of  deaf-mutism,  says  that  the  number  of 
deaf-mutes  in  Europe  is  estimated  at  about  i  in  1,350 
of  the  population.  In  England  the  frequency  (from 
statistics)  is  i  in  2,043,  Scotland  i  in  1,860,  Ireland 
I     in     1,398.      Seven     pedigrees    are     recorded,    but 


io8  HEREDITY  AND  EUGENICS 

there  is  no  separation  of  hereditary  and  acquired 
cases. 

Myoclonus  -  epilepsy,  marked  by  (degenerative) 
spasms  of  various  muscles,  is  also  a  disease  transmitted 
as  a  homogeneous  recessive  character.  One  of  the  most 
complete  of  family  studies  is  that  of  Lundborg  (191 3) 
on  a  farmer  family  in  Southern  Sweden  having  this 
affliction.  Among  the  2,232  individuals  examined 
he  groups  (i)  11  families  as  DDxRR,  with  166 
children  all  normal;  (2)  11  families  DRxDR,  with 
93  children,  of  which  jy  reached  an  age  of  over 
15  years.  Of  these,  24,  or  31-2  per  cent.,  were 
abnormal.  Applying  the  statistical  correction  of 
Weinberg  gives  21-8  per  cent,  abnormal  where  the 
expectation  is  25  per  cent.  (3)  DRxRR,  5  families 
with  46  children,  of  which  40  reached  over  15  3^ears 
of  age.  Twenty  of  these  were  normal,  or  45-3  per 
cent,  with  the  statistical  correction.  This  is  the  only 
Swedish  family  known  to  have  the  peculiarity,  and 
the  results  are  in  very  good  agreement  with  Men- 
delian  expectation. 

A  condition  which  is  said  to  be  rare  is  hereditary 
tremor.  Bergman  (1920)  states  that  fifty  families 
showing  this  condition  are  mentioned  in  the  literature. 
It  consists  in  rapid  involuntary  and  rhythmic  con- 
tractions of  certain  groups  of  muscles.  Usually  the 
arms  and  hands  are  affected,  but  sometimes  also  the 
head  or  legs  or  the  whole  body.  Hereditary  tremor 
most  frequently  appears  in  early  youth,  and  often 
increases  in  intensity  later.  It  generally  ceases  during 
sleep  and  perfect  rest.  Sometimes  it  appears  only 
in  connection  with  exertions  or  emotions.  The 
tremor  ma}^  be  rapid  (8  to  10  vibrations  per  second), 
or  slower  (3  to  4  per  second).  People  with  hereditary 
tremor  are  often  nervous  and  emotionall}-  unstable. 
The  handwTiting  is  affected,  and  may  be  almost 
or    quite    illegible.     Bergman    traces    this    condition 


PHYSICAL  CHARACTERS  IN  MAN        109 

through  three  generations  (four  individuals)  in  a 
Swedish  peasant  family.  The  condition  is  probably 
similar  to  paralysis  agitans,  which  is  said  to  be  due 
to  the  degeneration  of  the  parathyroid  gland. 

Ataxia  in  pigeons  is  apparently  a  very  similar 
condition.  In  1914  Riddle  (191 8)  obtained  in 
breeding  experiments  a  female  pigeon  with  marked 
lack  of  control  over  the  voluntary  movements  of 
head  and  body.  It  appeared,  probably  as  a  muta- 
tion, under  conditions  of  "  reproductive  overwork," 
in  which  the  bird  is  obliged  to  continue  laying  by 
removing  the  eggs;  and  the  condition  has  been  in- 
herited through  five  generations.  About  175  young 
have  been  reared,  and  of  this  number  1 19  were  classi- 
fied as  normal  and  46  as  affected.  From  these  and 
other  matings  the  evidence  indicates  that  ataxia  is 
inherited  as  a  simple  recessive  with  some  irregularities. 
Affected  birds  show  quivering  movements,  nodding 
heads,  unsteady  gait,  and  irregular  flight  in  various 
degrees.  Koch  and  Riddle  (191 8)  analysed  the 
brains  of  ataxic  birds  in  comparison  with  the  normal. 
They  found  in  the  former  higher  values  for  water 
content,  protein,  and  extractive  sulphur,  with  lower 
values  for  lipoids,  phosphatids,  and  cholesterol. 
The  results  suggest  a  chemical  immaturity  or  under- 
development of  the  affected  brain,  more  like  those 
of  normals  at  a  younger  stage  of  development,  but 
further  investigations  of  this  subject  are  desirable. 

In  the  mountains  of  Georgia  a  family  is  found 
(vStuckey,  191 6)  some  of  whose  members  for  four 
generations  have  had  constricted  eyelids.  The  sight 
is  normal,  yet  owing  to  this  constriction  it  is  necessary 
for  them  to  avert  their  heads  in  order  to  see.  The 
manner  of  inheritance  indicates  a  segregating  domi- 
nant character. 

Another  peculiar  case,  of  hereditary  nose  bleed, 
is   recorded   (Lane,    191 6),   members   of  a   famil}'   in 


no  HEREDITY  AND  EUGENICS 

Maine  showing  the  trait  through  three  generations. 
It  is  not,  hke  haemophiha,  sex-hnked.  It  manifests 
itself  by  spontaneous  bleeding  at  the  nose  almost 
daily,  beginning  at  the  period  of  adolescence  and 
continuing  until  eighteen  or  twenty.  Individuals 
showing  it  are  vigorous  in  health  and  grow  rapidly, 
often  feeling  discomfort  if  the  bleeding  does  not 
take  place. 

Diseases  like  haemophilia  (abnormal  tendency  to 
bleeding),  Gower's  disease  (saltatory  spasms),  and 
colour-blindness  are  well  known  to  be  sex-linked  in 
their  inheritance,  but  with  complications  in  the  last 
instance.  Bulloch  and  Fildes  (1910)  bring  together 
a  vast  amount  of  information  concerning  haemophilia, 
with  many  pedigrees.  Nasse  in  1820  asserted  that 
it  is  transmitted  entirely  by  unaffected  females  to 
their  sons.  Of  the  171  recorded  instances  of  trans- 
mission, belonging  to  forty-four  families,  sixty  conform 
to  the  "  law  of  Nasse."  In  the  eleven  other  families, 
in  some  of  which  inheritance  from  father  to  son  was 
supposed  to  have  taken  place,  there  is  no  good  evidence 
that  this  ever  took  place.  Such  apparent  cases  are 
found  to  be  explained  by  intermarriage  of  "  bleeder  " 
families  or  in  other  ways.  In  the  forty-four  families 
studied  there  were  644  males  to  464  females — a  great 
excess  of  males .  The  marriage-rate  of  males  in  bleeder 
families  is  ver}^  much  lower  than  of  females  (9-6  per 
cent.  :  36-8  per  cent.).  The  disease  is  rare.  Lenz 
(191 2)  gives  an  extensive  bibliography  of  haemophilia. 

Among  recessive  conditions  are  alkaptonuria*  and 
albinism.  The  most  extensive  pedigrees  of  cataract 
have  been  those  collected  by  Nettleship  {cf.  Bateson, 
1909).  They  show  that  various  forms  of  cataract 
are  usually  transmitted  as  dominants.  Harman 
(1910)  classifies  cataracts  as  lamellar,  axial,  stellate, 

*  A  condition  in  which  alkaptan  (probably  a  derivative  of 
tyrosin)  is  present  in  the  nrine. 


PHYSICAL  CHARACTERS  IN  MAN        iii 

and  polar.  Details  are  given  of  a  number  of  pedigrees 
of  inheritance,  but  no  attempt  is  made  to  draw  con- 
clusions regarding  the  manner  of  inheritance.  In 
another  paper,  however,  the  same  author  (Harman, 
1909)  cites  a  pedigree  of  live  generations  showing 
the  condition  to  be  a  Mendelian  dominant.  Parents 
who  are  normal  have  only  normal  children.  Of 
fifty-five  persons,  nineteen  were  known  to  be  affected. 
Others  who  w^ere  not  examined  probably  had  the 
defect  slightly.  Among  forty-one  persons  personally 
examined  or  certified,  nineteen  were  cataractous. 
This  is  very  close  to  the  expected  50  per  cent. 

The  indications  of  the  de  novo  origin  of  hereditar}' 
congenital  cataract  are  clearly  substantiated  by  the 
pedigree  of  a  family  whose  history  is  described  by 
Danforth  (191 4).  That  congenital  cataract  is  a 
dominant  character  has  been  disputed  by  Jones  and 
Mason  {ig\6a),  who,  from  a  discussion  of  Harman's 
data  in  the  Treasury  of  Human  Inheritance,  conclude 
that  it  is  a  simple  Mendelian  recessive.  This  con- 
clusion was  criticised  by  Danforth  (191 6),  who,  how- 
ever, did  not  hold  that  a  single  Mendelian  factor  was 
involved.  In  their  reply  Jones  and  Mason  (1916^^) 
conclude  that  it  is  impossible  to  arrive  at  a  satis- 
factory view  of  cataract  inheritance,  but  that  the 
hypothesis  of  a  single  Mendelian  recessive  is  the  one 
that  is  best  supported  by  the  facts  in  hand.  Detlefsen 
and  Yapp  (1920)  describe  a  case  of  congenital  cataract 
in  cattle,  which  they  conclude  behaves  as  a  simple 
Mendelian  recessive.  A  registered  Holstein-Friesian 
bull  inbred  with  his  own  stock  gave  a  number  of 
cataractous  offspring.  There  is  no  record  of  cataract 
in  any  of  the  ascendants.  To  unrelated  cows  this 
bull  produced  only  normal  calves.  But  thirty-two 
Fj  daughters  mated  to  an  Fj  son  gave  sixt^'-three 
calves,  fifty-five  of  which  were  normal  and  eight  had 
congenital  cataract  of  the  stellate  t3'pe. 


I  12 


HEREDITY  AND  EUGENICS 


An  early  record  of  sex-linked  colour-blindness 
(*'  Daltonism  ")  is  of  such  interest  that  it  is  included 
here.  It  was  communicated  to  the  Royal  Society  in 
1 778  by  the  Rev.  Michael  Lort,  and  consists  of  a  letter 
from  Mr.  J.  Scott  to  the  Rev.  Mr.  Whisson  of  Trinity 
College,  Cambridge,  describing  his  infirmity,  and 
stating  which  of  his  relatives  also  possessed  it.  This 
has  been  thrown  into  the  form  of  a  pedigree  chart 
by  Cole  (191 9),  from  whom  Fig.  20  is  taken  with 
modifications.      No.  III.  3    is   the  deponent,  and   it 


n 


in 


l^-^ 


L_J 


XYorXY 


ffi 


4 


XX 


k^ 


/,— . 


2,-s 


XYorXY 


XXorXX 


XY 


XY 


4.- 


XYorXY 


o 


XX 


4 


o 


XXorXX 


1 


XY 


XX 


XY  XY  XY  XX 

Fig.  20. — Pedigree  Chart  of  Colour-Blindness. 


will  be  seen  that  his  father  and  his  mother's  brother 
were  also  colour-blind.  His  mother,  though  normal, 
had  a  colour-blind  son  and  daughter,  and  she  must 
therefore  have  been  heterozygous  for  the  character 
(see  Fig.  8,  p.  23),  which  gives  the  history  of  the  sex 
chromosomes.  Homozygous  colour-blind  mothers 
transmit  the  defect  to  all  their  sons,  as  in  generation 
IV.,  while  normal  but  heterozygous  mothers  transmit 
it  to  half  their  sons. 

Fathers,   on   the  other   hand,   never   transmit   the 


PHYSICAL  CHARACTERS  IN  MAN        113 

defect  to  their  sons ;  but  half  their  daughters  by 
normal  mothers  will,  though  normal,  be  transmitters 
to  half  their  sons  by  a  normal  father.  Heterozygous 
mothers  with  a  colour-blind  father  will  have  50  per 
cent,  of  colour-blind  daughters  (while  all  the  daughters 
will  transmit  the  defect),  and  half  the  sons  of  such  a 
marriage  will  also  be  colour-blind.  Regarding  the 
deponent's  grandparents  there  is  no  record,  but  the 
grandmothers  must  both  have  been  either  colour-blind 
or  heterozygous  transmitters  of  the  defect,  while  the 
grandfathers  may  or  may  not  have  been  colour- 
blind. 

A  shorter  account  of  another  case  of  colour-blindness 
is  given  in  a  letter  written  in  the  previous  year  by 
Mr.  Joseph  Huddart  to  the  Rev.  Joseph  Priestley, 
and  published  in  the  Phil.  Trans.,  1777.  A  shoe- 
maker named  Harris  from  Maryport,  Cumberland, 
was  colour-blind,  having  discovered  it  at  the  age  of 
four  years  through  being  unable  to  distinguish  a  red 
stocking  from  an  ordinary  (presumably  black)  one. 
He  also  observed  that  "  when  young,  other  children 
could  discern  cherries  on  a  tree  by  some  pretended 
difference  of  colour,  though  he  could  only  distinguish 
them  from  the  leaves  by  their  difference  of  size  and 
shape."  Colour-blindness  consists  essentially  in  the 
failure  to  distinguish  red  from  green.  I'his  man 
"  had  two  brothers  in  the  same  circumstances  as  to 
sight;  and  two  other  brothers  and  sisters  who,  as  well 
as  their  parents,  had  nothing  of  this  defect."  Evi- 
dently the  mother  was  heterozygous,  and  transmitted 
the  defect  to  half  her  sons.  According  to  Bateson 
(1909),  in  European  countries  at  least  4  per  cent,  of 
the  male  population  and  less  than  0-5  per  cent,  of  the 
females  are  colour-blind. 

Bowditch  (1922)  describes  three  families  related 
through  marriage,  all  showing  the  usual  type  of 
sex-linked   inheritance.     In   one   of   the  families  the 

8 


1 14  HEREDITY  AND  EUGENICS 

condition  is  present  in  the  males  of  three  generations, 
being  transmitted  in  one  case  through  two  genera- 
tions of  females  before  reappearing  in  a  male.  In 
the  second  family  there  were  two  cases  of  colour- 
blind females,  one  of  whom  had  three  sons,  two  of 
whom  were  known  to  be  colour-blind. 

Little  and  Gibbons  (1921)  have  recently  considered 
the  inheritance  of  haemophilia  and  colour-blindness 
in  relation  to  the  presence  of  sex-linked  lethal  factors, 
which  would,  of  course,  follow  the  same  line  of  in- 
heritance. If  there  is  linkage  between  a  sex-linked 
lethal  factor  and  the  normal  allelomorph  to  haemo- 
philia or  colour-blindness  (the  latter  being  due  to 
different  defects  in  one  X  chromosome,  and  the  normal 
to  a  non-defective  X  chromosome),  then  the  authors 
show  that  there  should  be  an  excess  of  abnormals 
among  the  males  in  pedigrees  in  which  these  sex- 
linked  diseases  occur,  and  a  decreased  proportion  of 
females  in  families  in  which  an  excess  of  affected  males 
does  not  occur.  From  the  data  of  Bulloch  and 
Fildes  (1910),  as  well  as  other  data  at  the  Eugenics 
Record  Office,  they  find  these  expectations  fulfilled, 
thus  furnishing  evidence  of  sex-linked  lethal  factors 
in  man.* 

Congenital  stationary  night-blindness  w^as  recognised 
as  a  Mendelian  dominant  b}^  Nettleship  (1907). 
It  was  in  existence  near  Montpelier  as  early  as  1637. 
Data  were  afterwards  obtained  from  the  parish 
records,  and  in  1836  Cuvier  published  a  pedigree  of 
seven    generations.     The    Abbe    Capion    completed 

*  Lethal  factors  have  been  most  extensively  studied  in  Dvoso- 
phila.  Their  presence  causes  the  normal  development  to  go 
astray,  leading  to  the  death  of  the  organism  at  an  early  or  a  later 
stage  in  its  development.  Enriques  (191 9)  has  shown  that  in 
the  fly  Calliphora  erythrocephala,  certain  individuals  produce 
25  per  cent,  of  non-vital  offspring.  The  larvae  cease  to  eat  after 
two  or  three  days  and  then  die.  Some  of  the  non-lethal  offspring 
in  turn  produce  lethals  in  varying  proportions. 


PHYSICAL  CHARACTERS  IN  MAN        115 

these  records  and  added  later  ones,  making;  ten 
generations.  The  night-blinchiess  was  first  broiii^ht 
to  the  village  by  Jean  Nougaret,  who  was  born 
about  1637.  It  has  therefore  been  handed  down  for 
about  250  years  through  a  large  number  of  indi- 
viduals. Bateson  (1909,  p.  220)  gives  a  chart  of  this 
pedigree. 

In  another  family  studied  b}*  Newman  (191 3), 
night-blindness  (hemeralopia)  is  inherited  like  colour- 
blindness, as  a  sex-linked  character,  being  transmitted 
through  unaffected  daughters  of  affected  males  to 
some  of  their  sons.  This  family  is  from  Texas,  having 
originated  in  North  Carolina.  In  one  respect  it 
departs  from  the  t3^pical  scheme  for  sex-linked  in- 
heritance, in  that  there  is  "  apparent  non-inheritance 
of  the  capacity  to  transmit  night-blindness  on  the 
part  of  the  sisters  of  night-blind  men."  In  F3  and 
F5,  if  there  were  no  consanguineous  marriages,  there 
should  be  equal  numbers  of  females  carrying  or  not 
carrying  night-blindness.  But  none  of  the  five 
married  sisters  of  F3  night-blind  men  show  any 
trace  of  night-blindness  in  their  progeny.  Newman 
suggests  that  possibly  night-blindness  cannot  be 
inherited  through  two  successive  generations  in  the 
female  line,  owing  to  prolonged  association  of  the 
defective  X  (sex)  chromosome  with  a  normal  X. 
The  next  generation  will  determine  whether  this  is 
the  true  explanation. 

In  its  main  essentials  the  character  in  this  familv 
behaves  as  a  recessive  located  in  the  X  chromosome, 
but,  as  in  haemophilia,  there  is  an  excess  of  abnormals. 
Thus,  of  the  36  offspring  of  the  night-blind-carrying 
daughters  of  night-blind  men,  there  were  22 (j",  14?  , 
and  of  these  22,  17  were  affected  and  only  5  not.  In 
this  family  the  night-blindness  is  usually  accompanied 
by  m3^opia  (short-sightedness),  and  almost  invari- 
ably by  strabismus  (squinting),  Avith  frequent  occur- 


ii6  HEREDITY  AND  EUGENICS 

rence  also  of  pterygium.*  It  is  believed  that  all 
these  conditions  form  one  complex,  and  whether 
all  appear  may  depend  on  other  factors  present. 

Nettleship  (191 2)  has  also  described  a  family  in 
which  night-blindness  was  sex-linked  and  was  as- 
sociated with  myopia.  It  would,  therefore,  appear 
that  the  same  condition  may  arise  through  an  altera- 
tion in  the  sex  chromosome  or  in  another  chromosome. 

The  inheritance  of  manv  other  abnormalities  of  the 
eye  is  known.  For  example,  Folkar  (1909)  has  traced 
nodular  opacity  of  the  cornea  through  three  genera- 
tions, finding  nine  cases  abnormal  to  nineteen  normal 
or  unknown. 

A  bibliography  of  hereditary  eye  defects  has 
recently  been  published  b}^  Howe  (1921).  Among 
hereditar}^  defects  are  included  corneal  degeneration, 
coloboma  (congenital  fissure)  of  the  iris,  aniridia 
(absence  of  iris),  glaucoma  (a  disease  of  the  eye  wdth 
intense  intra-ocular  pressure,  resulting  in  hardness  of 
the  eye  and  blindness),  cataract,  congenital  disloca- 
tion of  the  lens,  retinitis  pigmentosa  (inflammation 
of  the  retina,  with  sclerosis,  pigmentation,  and  atrophy 
of  the  retina),  atrophy  of  the  optic  nerve,  micro- 
phthalmus  (abnormally  small  e3^es),  myopia  (short- 
sightedness), astigmatism  (a  defect  in  the  lens  of  the 
eye,  in  which  not  all  light  rays  are  brought  to  a  focus 
at  the  same  point),  nystagmus  (continuous  rolling 
movement  of  the  eyeball),  and  ptosis  (drooping  of  the 
eyelid  owing  to  paralysis). 

Briggs  (191  8)  has  studied  the  inheritance  of  ptosis 
(paralytic  drooping  of  the  eyelid)  through  six  genera- 
tions from  a  w^oman  having  this  ocular  defect.  The 
lineage  belongs  to  a  family  in  the  mountains  of  the 
vSouthern  States,  and  included   128  individuals,  half 

*  Congenital  pterygium  or  epitarsus  is  an  abnormality  of  the 
eye  in  which  there  is  a  fold  in  the  conjunctiva  or  membrane  lining 
the  eyelid  and  covering  the  front  of  the  eyeball. 


PHYSICAL  CHARACTERS  IN  MAN        117 

of  whom  had  the  defect.  Photographs  are  given, 
and  a  chart  indicating  that  the  character  is  a 
Mendehan  dominant. 

Nyctalopia  or  day-bhndness  is  also  said  to  be 
hereditary.  Sedgwick  (1861)  cites  a  case  of  moment- 
ary blindness  after  bending  their  heads  in  a  father 
and   two   sons.     He   also   refers   to   the   Le   Compte 

Q   X  %  Blind  at  35 
n  X    %  Blind  at  19 


1 


4     4  A   6    i 

bl.l3  bl.13     d-2       age  13     age  3    age  I 

Fig.  21. — Female  Sex-Linked  Blindness. 

family,  in  which  thirty-seven  children  and  grand- 
children became  blind,  like  the  grandfather,  at  the 
age  of  seventeen  or  eighteen  years. 

Two  interesting,  because  contrasted,  pedigrees  of 
amaurosis  or  hereditar}^  blindness  are  given  by 
Sedgwdck  (1863).     In  the  first  (Fig.  21)  the  condition 

i  *  i  i  ii  6  6  6 

Fig.  22. — Male  Sex-Linked  Blindness. 

is  apparently  confined  to  the  females,  wdio  go  blind 
before  middle  age.  In  the  second  the  same  con- 
dition is  confined  to  the  males  and  skips  a  generation 
in  inheritance  (Fig.  22). 

Several  pedigrees  of  sex-linked  inheritance  of  excep- 
tional interest  are  described  or  cited  b}^  Sedgwick 
(1861).     One    of   them    is    a    family  with   ichthyosis 


ii8 


HEREDITY  AND  EUGENICS 


(see  also  p.  122),  which  is  evidentl}^  transmitted  by 
females  to  half  their  sons,  as  indicated  in  Fig.  23, 
compiled  from  the  data  given. 

In  another  family,  cited  from  Cunier,  thirteen 
cases  of  ichthyosis  occurred  in  five  generations,  and 
all  the  affected  individuals  were  females.     Hence  the 

^  o 


n 
in 


IT 


f 


)xn 


ri 


7 


Fig.  23. — Pedigree  of  Male  Sex-Linked  Ichthyosis. 

condition  is  in  this  family  female  sex-linked.  The 
character  must,  therefore,  behave  as  a  dominant  in 
the  females  of  the  latter  family  and  as  a  recessive  in 
the  females  of  the  former  family. 

An  even  more  remarkable  case  of  female  sex-linked 
inheritance  is  described  by  Cunier  (1839),  in  which 


F 

4 

¥ 

• 

- 

n 
ni 

1 

2 

4x 

1 

IV 
V 

|J-,3         rJ-, 

4      rJL.5         X6 

*f= 

i'xD 


1^     4^xn    d 


i 


8 


Fig.  24. — Pedigree  of  Female  Sex-Linked  Colour-Blindness. 

colour-blindness  is  inherited  from  mother  to  daughter 
alone  through  five  generations  (see  Fig.  24)  in  a 
Belgian  family.  This  again  appears  to  be  because 
the  character  is  behaving  as  a  dominant  instead  of 
a  recessive. 

The    condition    is    transmitted    from    mother     to 


PHYSICAL  CHARACTERS  IN  MAN        119 

daughter  directly  in  the  female  line — that  is,  it  is 
sex-linked  or,  better,  female  sex-linked.  It  may  be 
spoken  of  as  matrilineal  in  descent .  The  appearance 
of  the  character  in  heterozygous  females  shows  it  to 
be  a  dominant.  We  may  think  of  such  females  as 
having  one  affected  and  one  normal  X  chromosome 
(see  p.  23).  This  would  be  transmitted  to  half  the 
sons,  none  of  whom  are  affected,  presumably  because 
the  presence  of  the  Y  chromosome  in  some  way 
neutralises  its  activity.*  Half  the  sons  should  then 
be  capable  of  transmitting  colour-blindness  to  all 
their  daughters.  Unfortunately  the  records  of  the 
family  furnish  no  data  regarding  the  male  lines  of 
descent  in  this  famil3\  But  it  seems  likely  that  if 
such  transmission  had  occurred  it  would  have  been 
noticed,  because  the  facts  are  evidently  carefully 
recorded.  It  is  possible,  therefore,  that  transmission 
through  the  males  may  fail,  just  as  it  appears  to  fail 
to  be  inherited  through  two  successive  generations 
in  the  female  line  in  the  night-blind  family  studied 
by  Newman  (191 3)  (see  p.  115).  Another  possible 
explanation  would  be  that  only  sons  who  have  re- 
ceived a  normal  X  chromosome  are  viable.  This 
should  lead  to  a  deficiency  of  males  in  the  offspring. 
It  is  very  interesting  to  find  colour-blindness  trans- 
mitted as  a  sex-linked  dominant  in  this  family  and 
a    sex-linked   recessive    in    others.     In    this    Belgian 

family  Madame  Th (III.  i.  Fig.  24)  and  her  aunt 

and  grandmother  could  not  distinguish  blue  from 
red  ("  rouge  "),  while  her  descendants  confounded 
blue  with  "  cerise."  The  eyes  of  affected  individuals 
were  very  sensitive  to  light. 

Sedgwick  (1861)  states  that  inability  to  distinguish 
colours  is  often  associated  with  inability  to  distinguish 

*  There  is  some  evidence  (see  p.  94)  that  in  man  and  in  fishes, 
unUke  insects,  the  Y  chromosome  plays  an  active  role  in  in- 
heritance. 


I20  HEREDITY  AND  EUGENICS 

sounds,  and  cites  a  famil}^  in  which  all  the  colour-blind 
members  were  also  stone-deaf.  He  also  describes  an 
interesting  famity,  here  thrown  into  pedigree  form 
(Fig.  25),  having  coloboma  iridis  or  cleft  iris.  This 
pedigree  is  difficult  to  explain,  for  it  not  only  shows 
transmission,  as  in  an  ordinary  male  sex-linked 
character,  through  an  unaffected  mother  to  half  her 
sons,  but  also  direct  transmission  from  father  to  son  in 
two  cases,  unless  the  waves  here  happened  to  be  trans- 
mitters. One  son  (III.  7)  only  had  the  defect  in  one 
eye.  vSedgwick  also  describes  cases  of  inheritance 
of  aniridia  (absence  of  iris),  amaurosis  (blindness), 
microphthalmia,  absence  of  eyes,  and  squinting. 
The   latter  is   due  to   defective  musculature  of  the 


I  Ox 


i^ 


nx6^     ¥ 


n  DxO        bao 

Fig.  25. — Family  showing  Cleft  Iris. 

eye,  and  is  stated  to  be  hereditary  in  some  families 
for  many  generations.  In  one  family  the  five  boys 
squinted  in  the  left  eye  or  in  both  eyes,  while  the  five 
girls  were  normal.  Their  father  and  mother  were 
normal,  but  the  mother's  sister  had  a  boy  and  girl 
both  squinting  with  the  left  eye. 

A  celebrated  case  which  is  often  referred  to  in  the 
early  literature  is  that  of  "  the  porcupine  man," 
Edw^ard  Lambert.  The  first  account  appears  to  be 
that  of  Machin  (1733).  A  countr}^  labourer  showed 
his  son,  who  was  then  fourteen,  in  London.  The  son 
had  a  very  scaly  skin  which  did  not  bleed  when  cut, 
but  was  callous  and  insensible.  The  skin  was  shed 
every  year  in  the  autumn,  a  new  skin  growing  up 


PHYSICAL  CHARACTERS  IN  MAN        121 

underneath.  It  had  "  bristly  parts  "  about  the 
belly  and  flanks,  which  rustled  like  the  quills  of  a 
hedgehog.  He  was  born  normal,  but  the  skin  began 
to  turn  yellow  at  the  age  of  seven  or  eight  weeks, 
then  by  degrees  changed  to  black,  then  thickened  and 
grew  into  its  present  condition.  The  parents  were 
apparently  normal  and  had  "  many  other  children," 
none  of  which  showed  this  deformity,  which  seems 
to  have  been  an  extreme  form  of  keratosis. 

Further  details  of  this  individual  are  given  (Baker, 
1755)  w^hen  he  was  about  forty  years  old.  The  skin 
most  nearly  resembled  "  an  innumerable  company  of 
warts,"  of  a  dark  brown  colour,  and  near  an  inch 
in  height  when  fully  developed.  His  head  and  face, 
palms  and  soles,  alone  were  free  from  this  condition. 
He  now  had  six  children,  all  with  the  "  same  rugged 
covering  as  himself,"  the  condition  making  its  first 
appearance  about  nine  weeks  after  birth.  The 
describer  draws  some  interesting  conclusions,  which 
we  may  quote  in  his  own  words  :  "  It  appears,  there- 
fore, past  all  doubt,  that  a  race  of  people  may  be 
propagated  by  this  man,  having  such  rugged  coats 
or  coverings  as  himself;  and  if  this  should  ever 
happen,  and  the  accidental  origin  be  forgotten,  'tis 
not  improbable  they  might  be  deemed  a  different 
species  of  mankind:  a  consideration  which  would 
almost  lead  one  to  imagine  that  if  mankind  were  all 
produced  from  one  and  the  same  stock,  the  black 
skins  of  the  negroes,  and  many  other  differences  of 
the  kind,  might  possibly  have  been  originall}^  owing 
to  some  such  accidental  cause."  In  modern  language 
we  should  call  this  individual  a  simple  dominant 
mutation,  like  so  many  of  the  other  abnormalities 
in  man. 

According  to  Sedgwick  (1861),  this  condition  was 
perpetuated  for  two  more  generations,  two  brothers 
of  the  fourth  generation  visiting  Germany  in   1802. 


122  HEREDITY  AND  EUGENICS 

They  had  seven  sisters  who  were  normal,  from  which  it 
would  appear  that  the  character  was  male  sex-linked — 
in  other  words,  recessive  or  suppressed  in  the  presence 
of  the  normal  X  chromosome  in  females,  and 
dominant  or  finding  expression  in  the  presence  of 
the  Y  chromosome  in  males. 

A  less  extreme  form  of  the  same  condition  (Martin, 
1818)  was  Jane  Holden,  aged  three,  whose  whole  skin 
except  the  face  w^as  "  covered  with  small  scales,  or 
rather  warty  or  bristle-like  projections,"  light  brown 
to  black  in  colour  and  constantly  exfoliated.  The 
condition  began  at  the  age  of  three  months.  Her 
mother  was  the  same,  except  that  the  neck,  breast, 
and  forearms,  as  well  as  the  soles  of  the  feet,  were 
free  from  this  condition.  Her  parents  were  healthy, 
and  she  was  the  only  one  of  six  children  having  the 
disease.  In  this  family,  unlike  the  previous  ones, 
the  condition  is  therefore  not  male  sex-linked. 

Still  less  severe  forms  of  ichthyosis  were  formerly 
said  to  be  rather  frequent  on  the  Continent,  and  were 
called  "pellagra."  Sedgwick  (1861)  quotes  Itahan 
statistics  among  the  peasants  of  Lombardy,  in  which, 
in  184  families,  there  were  671  healthy  individuals 
and  648  showing  pellagra.  From  this  it  would  appear 
that  the  condition  perhaps  involved  a  simple  Men- 
delian  recessive  character.  In  modern  studies  of 
pellagra  (see  Davenport,  191 6)  in  Italy,  the  United 
States,  and  elsewhere  the  essential  symptoms  appear 
to  be  inflammation  and  ulcerations  of  certain  areas 
(often  symmetrically  placed)  of  the  skin,  often  accom- 
panied by  diarrhoea  from  ulcerations  of  the  intestine. 
These  symptoms  are  due  to  the  presence  of  a  toxic 
agent,  which  may  also  induce  nervous  and  mental 
disturbances  in  some  individuals.  Variations  in 
these  symptoms  are  partly  due  to  differences  in  the 
hereditary  constitution  of  affected  individuals,  leading 
to   differences   in   the   susceptibility   or   resistance   of 


PHYSICAL  CHARACTERS  IN  MAN        123 

various  organs  to  the  toxin.  Davenport  considers 
that  pellagra  is  probably  communicable,  but  the 
history  of  the  disease  will  depend  entirely  upon  the 
constitutional  conditions  of  resistance  which  it  meets 
in  the  organs  of  the  body.  When  both  parents  are 
susceptible  to  the  disease,  nearly  half  the  children  are 
susceptible,  while  the  disease  affects  less  than  i  per 
cent,  of  the  whole  population  (statistics  from  Spartan- 
burg Co.,  South  Carolina).  The  high  incidence  in 
certain  strains  will,  then,  be  due  partly  to  infection, 
but  also  depends  upon  susceptibility,  for  susceptible 
and  non-susceptible  children  often  occur  in  the  same 
family.  Pellagra  thus  bears  certain  resemblances, 
from  an  inheritance  point  of  view,  both  to  tuber- 
culosis and  cancer,  and  perhaps  also  to  leprosy. 

It  was  formerly  widely  held  (Sedgwick,  1863)  that 
leprosy  was  hereditary,  but  that  it  descends  by 
collateral  lines,  and  frequently  skips  a  generation. 
There  is  probably  some  basis  for  this  view,  which 
deserves  careful  attention  from  modern  students  of 
this  disease.  The  lepra  bacillus  is  known,  just  as 
is  the  tubercle  bacillus,  but  there  may  be  constitu- 
tional differences  in  the  resistance  to  its  attacks. 

vSeveral  other  pedigrees  showing  sex-limited  in- 
heritance may  be  cited  from  a  large  mass  of  data 
furnished  by  Sedgwick  (1863).  Pityriasis  versicolor, 
a  skin  disease,  is  confined  to  the  males,  but  transmitted 
by  the  females  to  their  children  in  a  family  where  the 
grandfather,  his  three  sons,  and  nine  males  of  the  next 
generation  all  have  it.  In  another  family  numerous 
warts  on  the  hands  characterise  the  female  line  for 
two  generations,  the  mother  and  her  three  daughters 
having  them,  the  two  sons  normal. 

In  another  family  numerous  sebaceous  tumours 
on  the  scalp  occurred  in  a  mother,  her  daughter, 
and  granddaughter,  while  the  sons  were  free.  The 
brother's  daughters,  however,  have  them,  '*  as  well 


124 


HEREDITY  AND  EUGENICS 


as  several  cousins  of  different  degrees  of  relationship." 
Hence  the  condition  can  be  transmitted  through 
(unaffected)  inales.  This  woman's  mother,  grand- 
mother, and  female  relations  backwards  for  seven 
generations  were  similarly  affected.  "  No  female 
who  had  attained  her  tenth  year  of  age  was  without 
them,  whilst  none  of  the  males  in  the  family  ever  had 
them."  In  another  family  exactly  the  same  manner 
of  inheritance  occurred,  a  woman,  the  mother, 
mother's  mother,  and  so  on,  for  two  more  generations, 
all  having  scalp  tumours,  as  well  as  several  female 
first  and  second  cousins  on  the  mother's  side.     Again 


ixn 


¥ 


^n 


i^i 


W~¥^^.6^ 


/<? 


/2 


d.3     9 


2k.     15 


13 


D 

5 


Fig.  26. — Family  showing  Early  Decay  of  Teeth. 
The  numbers  beneath  are  the  respective  ages  of  the  children. 


all  the  females  and  none  of  the  males  developed  the 
condition. 

A  striking  case  of  abnormal  early  decay  and  loss 
of  the  teeth  in  three  generations  of  a  family  is  given 
by  Sedgwick  (1863).  It  is  confined  to  the  females 
(see  Fig.  26),  and  there  is  no  evidence  as  to  whether 
it  is  transmitted  by  the  males. 

Among  family  peculiarities  which  are  known  to  be 
inherited,  one  of  the  most  notable  is  the  large  lower 
lip  and  prognathous  jaw  of  the  Hapsburgs.  Bateson 
(1909)  first  suggested  that  this  peculiarity  was  a 
Mendelian  dominant,  and  Haecker  (191 1),  from  a 
study  of  numerous  portraits,  confirms  this  conclusion. 
The  peculiarity  dates  back  at  least  to  Duke  Ernst  the 


PHYSICAL  CHARACTERS  IN  MAN        125 

Iron,  who  died  in  1424,  and  it  has  been  handed  clown 
continuously  to  the  present  time,  hence  for  a  period 
of  probabh^  more  than  500  years,  or  fifteen  to  twenty 
generations.  The  condition  is  less  marked  in  the 
women,  and  Haecker  interprets  it  as  the  result  of 
the  loss  of  an  inhibitin£>:  factor  which  normally  reiiu- 
lates  in  Europeans  the  development  of  the  lower 
lip  and  jaw.  At  least  one  other  sporadic  case  of 
prognathism  is  known  to  me,  but  I  am  not  aware 
of  any  other  data  concerning  its  inheritance.  In 
this  case  the  father  has  the  peculiarity,  while  one  of 
four  children  has  it  in  an  extreme  degree  and  two 
others  to  a  less  degree.  This  type  of  prognathism 
suggests  a  mild  form  of  the  condition  seen  in  the  bull- 
dog— a  mutation  which  also  occurs  in  cattle,  foxes, 
and  other  mammals.  Donitz  (1868),  for  example, 
describes  a  fox  skull  shaped  like  a  bull-dog's,  w^ith 
a  short  snout  and  the  mandible  turned  up  in  front 
of  the  premaxillse.  See  also  Ktihn  (1877)  and  Mivart 
(1890),  where  much  other  information  concerning 
variations  in  dogs  and  other  Canidae  will  be  found. 

Variations  of  the  type  just  mentioned  we  now  call 
parallel  mutations  (see  Gates,  1921,  chap,  v.),  since 
they  result  from  similar  changes  in  the  germ  plasm. 
The  list  of  such  cases  in  mammals,  given  in  Table  IV., 
is  taken  chiefly  from  Davenport  (191 6),  who  further 
points  out  that  rabbits  and  guinea-pigs  both  show 
agouti,  yellow,  chocolate,  black,  albino,  and  other 
colours.  Also  the  Angora  t3^pe  of  coat  is  found  in 
rabbits,  guinea-pigs,  cats,  dogs,  goats,  sheep  (Lincoln), 
and  others. 

The  medical  and  anatomical  literature  on  the  subject 
of  the  inheritance  of  abnormalities  in  man  is  much 
too  extensive  to  consider  here.  Only  a  few  cases, 
where  the  manner  of  inheritance  through  several 
generations  is  known,  are  included.  But  in  a  great 
number   of  other   pathological   and   anatomical   con- 


126 


HEREDITY  AND  EUGENICS 


ditions,  no  doubt,  further  research  would  disclose 
equalty  extensive  pedigrees  of  inheritance.  Hope  and 
French  (1908)  describe  a  family  in  which  persistent 
hereditary  oedema  (sw^elling  due  to  the  effusion  of 
water}^   liquid   into   the   connective  tissue)  is   traced 


TABLE  IV. 
Comparative  Table  of  Saltations. 


I 

2   '3    4    5  '6 

7 

8  19  10 

II 

Horses. 
Cattle. 

d 

4= 
C/3 

c 

Q 

if. 

a 
1^ 

0 

1.  Proopic  brachycephaly,  abbre- 

viation of  face 

2.  Sudden  development  of  "horns" 

on  hornless  races 

3.  Absence   of    horns    on   horned 

races 

4.  Jaw  appendages 

5.  Taillessness,  absence  of  caudals 

6.  Short-leggedness,   or  limb  ab- 

breviation    .  , 

7.  Consolidation  of  paired  hoofs, 

syndactylism 

8.  Polydactylism .  . 

9.  Epidermal  thickenings 

10.  Mottled  skin  markings 

11.  Excessive     hairiness    or    long 

hair    .  . 

12.  Hairlessness,  entire  absence  of 

hair    .  . 

13.  Excessively  fine  or  silky  hair 

14.  Reversed  hairs 

15.  Curled  hair 

XXXX         X         XXXX         X         XX                         X 

* 

X 
X 

X 
X 

X  t  X 

X 

X       X 

X 

X       X 

X       X 

X  X 
X 
X 

X 

X 
X 
X 

X 
X 

X 

X 
X 

X 
X 

X 

X 
X 

X 

X 

X 
X 

X 
X 

X 

X 

X 

X 
X 

X 
X 

X 

X 
X 
X 

X 

y 

X 

*  See  p.  215. 


I  Chinese  polo  ponies. 


through  five  generations,  appearing  in  thirteen  out  of 
forty-two  individuals.  This  w^as  accompanied  by 
nervous  attacks  in  many  cases.  The  inheritance,  as 
shown  by  the  pedigree,  is  in  accord  with  that  of  a 
Mendelian  dominant,  except  that  one  normal  female 


PHYSICAL  CHARACTERS  IN  MAN        127 

has  an  abnormal  child  in  a  family  of  six.  The  swelling;- 
of  the  legs,  which  was  extreme  in  certain  cases,  was 
usually  kept  down  by  w^earing  bandages.  vSeveral 
individuals  lived  to  over  sevent}'  with  their  legs 
bandaged,  having  had  the  malady  for  sixty  years  or 
more.  This  condition  w^as  first  described  by  Milroy  in 
America,  where  it  was  traced  through  six  generations, 
and  similar  cases  of  hereditary  oedema  have  been 
described  in  France  and  England.  Bulloch  (1909) 
gives  nine  pedigrees  of  trophcedema  (with  permanent 
swelling  of  feet  and  legs),  and  finds  it  rather  more 
common  in  females  than  in  males.  In  a  total  of 
seventy-three  affected  individuals  observed,  forty-one 
were  of  the  former  sex  and  thirty-tw^o  of  the  latter. 
Bulloch  (1909)  also  describes  angioneurotic  oedema,* 
or  acute  circumscribed  oedema,  in  which  there  are 
local  swellings  of  the  limbs,  trunk,  and  face,  and 
the  mucous  membranes  may  also  be  involved.  The 
swellings  are  temporary,  but  often  show  remarkable 
periodicity.  There  is  direct  inheritance  in  a  number 
of  instances,  or  the  disease  may  occur  as  a  family 
complaint. 

Gossage  (1908)  cites  many  instances  of  inherited 
abnormalities.  Ichthyosis  (a  dry,  rough,  and  scaly 
skin),  or  keratosis  (horny  growths  forming  warts  or 
callosities)  of  the  palms  or  soles  is  a  Mendelian 
dominant,  and  has  apparentl}^  originated  de  novo 
in  two  cases,  one  such  woman  having  twelve  chil- 
dren, all,  hke  herself,  abnormal.  Multiple  hereditary 
telangiectasis  (dilatation  of  the  capillaries  and  minute 
arteries)  is  apparently  a  dominant,  but  appears  late: 
fourteen  abnormals  to  twenty-seven  normals  were 
recorded.  Other  cases  given  are  inheritance  of 
(i)    tightly    curled    woolly    hair;    (2)    epidermolysis 

*  This  is  a  condition  in  which  there  is  swelling  in  patches  by 
the  accumulation  of  blood  in  the  connective  tissue  owinj^  to  a 
disorder  of  the  vasomotor  system  affecting  the  bloodvessels. 


128  HEREDITY  AND  EUGENICS 

bullosa  (a  loosened  state  of  the  epidermis,  with 
formation  of  deep  -  seated  buUse  or  blisters) ; 
(3)  bullosa;  (4)  early  baldness  with  monilithrix  (hairs 
brittle  and  with  bead-like  enlargements);  (5)  hypo- 
trichosis congenita  familiaris  (children  born  without 
hair,  or  losing  it  a  few  months  after  birth) ;  (6)  enlarged 
spleen;  (7)  polyuria  or  polydipsia  (excessive  secretion 
of  urine  containing  increased  amounts  of  solid  con- 
stituents); (8)  porokeratosis  (a  skin  disease  charac- 
terised by  hypertrophy  of  the  corneous  layer  followed 
by  inward  atrophy),  etc. 

Polyuria  or  diabetes  insipidus  is  a  condition  in 
which  the  kidneys  fail  to  function  properly,  so  that 
the  individual  passes  great  quantities  of  urine  of  low 
specific  gravity.  This  causes  excessive  thirst,  and 
makes  it  necessary  for  the  patient  to  drink  gallons  of 
water  dail}^  The  condition  may  be  either  congenital 
or  acquired.*  It  is  hereditary  in  a  number  of  cases. 
In  Weil's  case,  cited  by  Bulloch  (1909).  J-  ?•  Schwarz 
was  born  in  1772  in  Oberhessen,  and  had  220  de- 
scendants in  four  generations.  Thirty-four  of  them 
had  diabetes  insipidus.  Three  of  his  5  children  had 
the  affection,  7  of  his  29  grandchildren  had  it,  13  of 
his  66  great-grandchildren,  and  11  of  his  119  great- 
great-grandchildren.  In  four  of  the  larger  families, 
taken  from  the  fourth,  fifth,  and  sixth  generations,  the 
numbers  of  normals  and  abnormals  were  respectively  : 
4:4,  2:4,  2:3,  and  3:4,  making  a  total  of  11:15. 
Hence  the  condition  is,  as  usual,  a  Mendelian 
dominant.  In  this  pedigree  it  never  skips  a  genera- 
tion, except  in  one  recorded  instance  of  an  affected 
son  (died  age  three)  with  normal  parents.  Occa- 
sionally other  instances  of  skipping  a  generation  are 

*  This  is  an  excellent  example  of  the  same  peculiar  character 
being  hereditary  or  not  according  to  the  manner  of  its  origin — 
i.e.,  as  the  result  of  a  germinal  change  or  an  impressed  modifi- 
cation. 


PHYSICAL  CHARACTERS  IN  MAN        129 

recorded.  Probably  in  such  cases  some  favourable 
condition  in  the  transmitting  parent  prevents  the 
disease  appearing. 

Darwin,  in  his  chapter  on  Inheritance,  in  the 
Variation  of  Animals  and  Plants  under  Domestication, 
refers  to  man}^  cases  of  inherited  abnormalities  in 
man,  but  the  knowledge  of  his  time  was  insufficient 
to  explain  them,  as  they  can  now  be  clearly  under- 
stood in  the  great  majority  of  instances.  He  clearly 
recognises  this  when  he  states,  *'  The  laws  governing 
inheritance  are  quite  unknown." 

Differences  essentially  chemical  are  also  involved 
in  many  instances.  The  method  of  serum  formation 
and  precipitation  has  been  used  as  a  means  of  testing 
genetic  relationships,  both  in  animals  and  plants. 
Learmonth  (1920)  has  made  certain  interesting 
observations  in  this  connection.  Human  sera  have 
been  classified  into  four  groups,  according  to  their 
iso-agglutination*  reactions.  From  a  study  of  the 
iso-agglutinins  in  the  blood  of  forty  families  of 
parents  and  children,  it  is  concluded  that  tw^o 
Mendelian  factors,  A  and  B,  are  concerned.  Group  I. 
contains  both  factors,  group  II.  contains  A,  group  III. 
B,  and  group  IV.  neither.  These  differences  account 
for  the  violent  reactions  which  frequentl}'^  occurred 
after  blood-transfusion  before  the  introduction  of 
blood-compatibility  tests,  since  transfusion  can  only 
take  place  safely  between  members  of  the  same  group. 
With  further  experience  the  method  will  provide,  in 
many  cases,  a  test  of  the  paternity  of  a  child. 

Among  hereditary  abnormalities  referred  to  b}' 
Windle    (1891)    is    polymastia    or   accessory   breasts, 

*  An  iso-agglutinin  is  an  agglutinin  capable  of  agglutinating 
the  red  blood  corpuscles  of  other  individuals  of  the  same  species 
as  that  in  which  it  is  developed.  It  is  formed  in  the  blood  of  an 
animal  by  injection  of  the  blood  of  another  animal  of  the  same 
species. 

9 


I30  HEREDITY  AND  EUGENICS 

present  in  several  cases  in  mother  and  child;  hyper- 
trichosis or  excessive  hairiness,  which  is  said  to  be 
usually  associated  with  deficient  dentition ;  and  gluteal 
prominences,  a  racial  character  in  Hottentot  women. 
Congenital  luxation  (dislocation)  of  the  femur  was 
traced  through  five  generations,  and  on  both  sides 
of  the  house.  Cleft-palate  and  hare-lip  are  said  to  be 
undoubted^  hereditary,  but  many  more  data  con- 
cerning their  inheritance  are  required.  Rischbieth 
(1910),  in  a  study  of  these  malformations,  collated 
the  data  regarding  their  incidence.  They  are  often 
associated.  Frobelius  examined  180,000  children  in 
the  Foundling  Hospital  of  St.  Petersburg  during 
thirty  years,  and  found  one  or  both  conditions  in  a 
total  of  1 1  8  cases,  br  o-o66  per  cent.  Among  67,945 
children  examined  at  London  Hospital  in  1908, 
thirt3'-nine  showed  the  deformity  in  one  form  or 
another,  hence  a  frequency  of  0-057  P^^*  cent.  But 
this  figure  is  too  low,  because  some  children  attended 
more  than  once.  The  condition  is  said  to  be  more 
common  among  defectives,  and  it  is  often,  though  not 
always,  associated  with  other  deformities.  \ 

Of  similar  origin  are  branchial  fistula  (failure  of 
the  branchial  clefts  in  the  neck  to  close  before  birth), 
and  hypospadias  (abnormal  opening  of  the  urethra), 
both  of  which  show  signs  of  being  hereditary.  Eden- 
tulism  or  partial  absence  of  teeth,  sometimes  accom- 
panied b}'  a  peculiarity  of  the  hair,  is  hereditary, 
and  was  traced  through  four  generations  in  one  family, 
being  accompanied  by  inherited  polydactylism  in 
the  fourth  generation.  Among  malformations  of  the 
eye,  instances  are  quoted  of  microphthalmus,  absence 
of  iris,  coloboma  (failure  to  close  choroidal  fissure), 
congenital  dislocation  of  the  lens,  and  strabismus 
(squinting)  being  inherited  through  several  generations. 

There  are  many  early  records  of  hermaphroditism 
or  allied  conditions  in  man,  many  of  which  would 


PHYSICAL  CHARACTERS  IN  MAN        131 

now  be  classed  as  intersexual.  Metchnikoff  (1903) 
concludes,  from  the  presence  in  each  sex  of  traces  oi 
the  sexual  organs  belonging  to  the  other  sex,  that  at 
a  very  remote  period  the  ancestral  vertebrates  were 
hermaphroditic,  and  that  the  sexes  have  only  gradu- 
ally become  separated  since.  This  is,  however,  a 
ver}"  doubtful  line  of  reasoning.  Bulloch  ( 1 909)  shows 
that  in  man  the  condition  may  occur  in  several 
members  of  a  family  or  in  several  generations,  a  fact 
which  was  known  to  Bauhin  as  earl}*  as  161 4.  But 
the  known  pedigrees  are  incomplete,  and  little  is 
known  of  its  inheritance.  Blacker  and  Lawrence 
(1897)  and  Lawrence  (1906)  discuss  the  cases  of 
"  true  hermaphroditism  "in  man.  Thirty-three  cases 
of  hermaphroditism  (intersexualit}')  are  on  record  in 
the  medical  literature.  Of  these  only  five,  and  one 
which  the  authors  describe,  are  regarded  as  true 
hermaphrodites,  defining  the  condition  as  one  in 
which  the  specific  tissues  of  both  ovary  and  testis 
are  present  in  any  amount.  Anatomical  details  of 
these  six  cases,  which  vary  greatly,  are  given.  Xo 
other  cases  are  regarded  as  fully  proven.  Human 
gynandromorphs,  having  male  secondary  sexual 
characters  on  one  side  of  the  bodv,  and  female 
secondar}^  sexual  characters  on  the  other,  are  not 
unknown.  Klebs  classified  "  hermaphrodites  "  as 
unilateral,  bilateral,  and  lateral. 

In  these  individuals  there  is  frequenth'  a  tendency 
for  transformation  from  one  sex  towards  the  other 
during  the  lifetime  of  the  individual,  as  shown  both 
in  behaviour  and  by  anatomical  examination.  That 
hens  with  diseased  ovaries  take  on  male  characters 
is,  of  course,  well  known.  It  is  not  our  purpose  to 
discuss  the  various  causes  and  phenomena  of  inter- 
sexuality  here,  but  it  ma}'  be  pointed  out  that  there 
are  several  types  of  intersexualit}'  in  animals,  in  some 
of  which  there  is  transformation  from  one  sex  to  the 


132  HEREDITY  AND  EUGENICS 

other,  while  in  others  the  intersexual  condition  is 
constant.  Juhan  Huxle}^  (1922)  has  discussed  this 
subject.  In  Drosophila  (Bridges,  1921)  the  sexual 
condition  is  shown  to  depend  on  a  particular  balance 
between  the  XY  chromosomes  and  the  ordinar}^ 
chromosomes  (autosomes),  as  shown  by  the  fact  that 
triploid  individuals  receiving  only  XX  chromosomes 
through  non-disjunction  are  not  females  but  inter- 
sexes, while  triploids  with  XXX  chromosomes  are 
ordinary  females.  Banta  (191  8),  from  his  studies  of 
sex  intergrades  in  Cladocera,  concludes  that  maleness 
and  femaleness  are  not  mutually  exclusive  states,  but 
that  strains  representing  every  quantitative  intergrade 
may  be  found.  Crew  (1921)  and  Witschi  (1921)* 
have  shown  that  in  frogs  a  real  transformation  from 
females  with  ovaries  to  males  occurs,  and  Crew  in  his 
studies  obtained  the  remarkable  result  that  such  a 
transformed  female  mated  with  an  ordinar}'  female 
produces  only  females  (774  offspring  examined  in 
tadpole  and  frog  stage).  This  is,  no  doubt,  because, 
notwithstanding  the  somatic  modification  of  a  female 
to  a  male,  the  structure  of  the  germ  plasm  and  the 
chromosome  content  (XX  chromosomes)  remain 
unchanged.  It  is  not  in  this  direction  that  any 
practical  application  to  the  human  race  is  to  be 
sought. 

Shattock  and  Seligman  (1906)  describe  a  case  of 
hermaphroditism  in  a  two-year-old  Leghorn  fowl. 
The  bird  laid  no  eggs  and  did  not  crow,  but  it  had 
the  comb,  wattles,  and  spurs  of  a  male,  but  not  its 
tail  feathers.  Both  male  and  female  genital  ducts 
w^ere  present,  with  an  ovotestis  on  the  left  side,  and 
apparently  a  testis  on  the  right  side.     The  authors 

*  Swingle  (1922)  controverts  Witschi' s  claim  to  have  trans- 
formed female  frogs  into  males,  showing  that  "  appeal  to  the 
somatic  sex  characters  completely  fails  as  proof  of  the  trans- 
iormation  of  female  frogs  into  males." 


PHYSICAL  CHARACTERS  IN  MAN       133 

discuss  the  occurrence  of  hermaphroditic  conditions 
in  reptiles,  amphibians,  fishes,  and  cyclostomata. 
Hanna  (1921)  states  several  interesting  facts  regard- 
ing hermaphroditism  in  seals.  It  is  a  rare  condition 
in  mammals,  and  has  not  been  previously  recorded 
in  seals.  Among  33,000  male  seals  killed  on  the 
Pribiloff  Islands  of  Alaska  in  191  8,  two  were  found 
to  be  hermaphrodites. 

An  American  family  is  described  by  Goldsmith 
(1922)  in  which  there  are  two  round  openings  in  the 
parietal  bones  at  the  back  of  the  skull.  These 
sometimes  form  a  single  opening  in  the  younger 
stages,  and  in  some  cases  it  may  later  close  up  entirely. 
It  is  clearly  a  failure  to  complete  development.  In 
five  generations  of  this  family  sixteen  cases  are  known. 
The  manner  of  its  inheritance  is  not  clear.  Micro- 
cephalic people  occasionally  occur  in  families  (Bern- 
stein, 1922).  There  is  often  more  than  one  such 
child  in  a  family,  but  they  seldom  occur  in  successive 
generations,  and  nothing  appears  to  be  known  con- 
cerning the  inheritance  of  this  condition. 

Absence  of  the  external  ear  is  cited  (Windle,  1891) 
in  a  case  where  a  normal  father  had  a  son  with  the 
defect.  The  father's  male  cousin  had  the  defect, 
and  two  of  his  male  children,  but  a  daughter  was 
normal.  A  Mendelian  dominant  is  suggested,  a 
result  which  is  especially  interesting  in  the  light  of 
recent  experiments  with  earless  sheep,  given  below. 
Sedgwick  (i  861)  cites  a  case  of  a  boy  with  no  external 
left  ear,  the  meatus  being  imperforate.  This  boy's 
father  had  a  male  cousin  whose  tw^o  sons  exhibited 
a  deficiency  of  the  cartilage  of  the  left  ear,  while  the 
daughter  was  normal.  The  manner  of  inheritance 
is  not  clear,  except  that  it  is  from  the  original  great- 
grandparents,  and  it  is  confined  to  one  side  of  the 
head.  In  another  case  a  woman,  two  of  her  daughters, 
and    two    granddaughters   had   rudimentary   lobules 


134  HEREDITY  AND  EUGENICS 

to  their  ears,  the  male  children  and  grandchildren 
being  normal.  The  rudimentary  lobules  probably 
represent  the  heterozygous  condition,  but  there  is  not 
sufficient  evidence  of  sex-linkage.  Sedgwick  (1863, 
p.  457)  describes  a  line  of  descent  in  three  generations 
with  rudimentary  ear-lobes  adherent  to  the  head. 
The  condition  appears  to  have  occurred  onl}^  in  the 
women.  It  was  present  in  the  grandmother,  in  two 
of  her  daughters,  the  third  not  being  examined,  and 
one  of  the  two  sons  examined  being  normal.  One  of 
the  daughters  who  had  the  peculiarity  transmitted 
it  to  her  two  daughters,  the  son  being  normal.  No 
doubt  many  other  ear  peculiarities  are  inherited. 
The  Kalmucks  are  said  to  have  large  and  unsightly 
ears  as  a  racial  character. 

Lynch  (1921)  describes  a  mutation  in  the  house- 
mouse,  in  which  the  ears  are  about  half  the  normal 
length  and  somewhat  narrower.  They  also  differ 
somewhat  from  the  normal  in  outline,  and  are  held 
close  to  the  head.  The  character  behaves  as  a  simple 
Mendelian  recessive. 

Ritzman  (1921)  has  found  that  short,  thick  ears 
in  a  breed  of  sheep  is  a  heterozygous  condition,  giving 
equal  numbers  of  both  types  of  offspring  in  crosses 
with  the  normal  (sixteen  short  ear:  sixteen  long  ear). 
The  mating  together  of  short-eared  individuals  has 
produced  an  earless  ram,  which  therefore  clearly 
represents  the  pure  recessive  condition.  Similar 
results  have  been  independently  obtained  by  Wriedt 
(191 9,  1 921),  who  adds  that  an  earless  ram  mated 
with  normal  sheep  gave  five  offspring  with  short  ears, 
while  an  earless  sheep  mated  with  a  normal  ram  pro- 
duced one  lamb  with  short  ears.  Earless  individuals 
mated  together  gave  earless  offspring.  Short  ears 
in  sheep  were  said  to  be  very  common  formerl}^  in 
Norway,  and  are  still  found  in  various  parts  of  the 
country.     There  is  evidence  that  both  the  short-eared 


PHYSICAL  CHARACTERS  IN  MAN        135 

and  earless  conditions  are  found  also  in  the  Karakul 
breed  of  Bokhara. 

Lush  (1922)  describes  the  inheritance  of  a  notch 
in  the  lower  margin  of  the  ear  in  cattle.  This  character 
is  found  in  a  Jersey  bull  at  the  Texas  Agricultural 
Experiment  Station,  and  is  inherited  as  a  simple 
dominant,  the  bull  (Gamboge's  Raleigh)  being  hetero- 
zygous. Thirty  of  his  calves  were  examined  and 
twelve  found  to  be  without  the  notch.  There  is  much 
variation  in  the  degree  of  expression  of  the  notch. 

As  an  example  of  the  inheritance  of  a  slight 
peculiarity  may  be  cited  the  case  of   a    bilobed  ear 


i 


o 


i 


B^ 


A 


\ 


B, 


i  6  i  i 


A  B2      B 

Fig.  27. — Pedigree  Chart  showing  Inheritance  of  Right 

Bilobed  Ear. 


described  by  Schofield  (191 7).  In  this  family  the 
condition  has  been  transmitted  through  four  genera- 
tions, only  the  right  ear  having  the  peculiarity.  The 
accompanying  chart  (Fig.  27)  shows  its  incidence. 
One  generation  or  even  two  may  be  skipped,  and  the 
condition  varies  considerably  in  different  individuals. 
Thus,  in  A  there  is  a  very  marked  deep  cleft  of 
considerable  length,  while  in  those  marked  B  the 
cleft  is  not  so  well  marked.  In  BB  it  was  only  a 
furrow,  while  in  B^  and  B,  there  is  a  deficiency  of 
hearing  in  the  bilobed  ear.  The  family  with  pitted 
ear-lobes,  described  by  Jenks  (191 6),  is  a  similar  case. 


136 


HEREDITY  AND  EUGENICS 


Kindred  (1922)  gives  the  pedigree  of  another  family, 
in  which  a  pecuhar  httle  pit  occurs  in  the  skin  at  the 
proximal  end  of  the  upper  part  of  the  helix  of  the 
left  ear.  This  is  known  to  have  occurred  in  four 
generations,  as  is  shown  by  the  chart  (Fig.  28). 

The  propositus  (III.  7)  has  the  pit,  as  well  as  her 
father  and  father's  father.  Some  of  her  father's 
brothers  and  sisters  probably  had  the  mark,  because 
some  of  her  cousins  were  known  to  have  it.  Three  of 
her  sisters  who  married  all  had  one  or  more  children 
showing  the  mark,  although  tw^o  of  them  did  not  have 
the  pit  themselves.  One  of  the  most  remarkable 
features  of  these  slight  peculiarities  is  their  unilateral 


n      ,(> 


5O 


i  ©  ©    ®     ©     © 


w  6,  6^ 6,  k^  h,  6e     6,  4m^ 


/O    ^/l     ^12  ^13 


W  ^//     ^12 


i, 


14 


*I3 


Fig.  28. — Pedigree  Chart  showing  Inheritance  of  a  Small 

Pit  in  the  Left  Ear. 


occurrence,  being  confined  to  the  right  side  in  one 
family,  and  the  left  in  another.  We  are  at  present  at 
a  loss  to  picture  the  hereditary  mechanism  by  which 
this  comes  about. 

Of  a  similar  nature  is  the  case  (Sedgwick,  1863)  of 
a  Spanish  nobleman  who  had  one  cheek  bigger  than 
the  other.  His  father  and  some  of  his  uncles  had 
the  same  peculiarity.  Another  record  of  the  same 
writer  (p.  464)  is  that  of  a  patient  in  St.  George's 
Hospital  in  1833.  Neither  he  nor  his  father  nor 
grandfather  had  a  patella  (knee-cap). 

Drinkwater  (191 4)  described  an  interesting  case  of 
bimanual  synergia,  in  which  the  individual  is  obliged 


PHYSICAL  CHARACTERS  IN  MAN       137 

to  move  both  hands  and  arms  in  the  same  direction 
at  the  same  time.  Only  four  other  cases  of  this  rare 
condition  are  known  in  the  medical  literature,  and 
they  were  all  recorded  in  Germany.  In  Drinkwater's 
case,  if  the  bo}^  held  a  pencil  in  each  hand  and  wTote 
with  the  right  hand,  the  left  would  produce  the 
same  words  in  mirror  image  form.  Attempts  to  move 
one  hand  when  the  other  was  held  caused  acute  pain. 
This  case  was  unique  in  that  the  synergia  was  accom- 
panied by  similar  sensations  in  both  hands  w^hen  only 
one  was  stimulated,  the  unstimulated  member  feeling 
the  sensation  more  intensely.  Crossing  of  sensations 
also  occurred.  Thus,  when  a  hot  test-tube  was  held 
in  the  right  hand,  and  a  cold  one  in  the  left,  the  left 
hand  felt  hot  and  the  right  cold. 

The  motor  phenomena  in  this  case  were  traced 
through  nine  individuals  occurring  in  four  generations. 
The  manner  of  inheritance  is  in  harmony  with  that  of 
a  Mendelian  dominant,  except  that  one  w^oman,  four 
of  whose  ten  children  showed  the  condition,  did 
not  exhibit  it  herself.  She  probably,  however,  was 
affected  in  infancy  and  outgrew  it.  Every  infant  has 
to  learn  to  use  its  right  and  left  limbs  independently, 
and  this  power  of  unilateral  control  develops  earlier 
in  some  individuals  than  in  others.  One  boy  in  this 
pedigree  w^as  able  to  overcome  the  synergia  at  the  age 
of  fifteen  years,  after  repeated  efforts.  The  condition 
is,  then,  essentially  one  of  failure  in  development  of  a 
particular  function. 

Among  many  inherited  peculiarities  of  the  blood 
system  may  be  mentioned  one  cited  by  Windle  (i  891 ) 
from  the  Chicago  Med.  Joitrn.  and  Exa))i.,  1879, 
p.  475.  The  radial  arter}'  of  a  male  in  both  arms 
passed  over  the  supinator  longus  muscle  at  3  to  4  cm. 
above  the  wTist,  and  ran  over  the  radial  extensors 
above  the  styloid  process  to  its  normal  distrilnition. 
All  his  children  had  the  same  abnormalit}'  on  tlie  left 


138  HEREDITY  AND  EUGENICS 

side,  and  the  daughters  transmitted  it  better  than  the 
sons.  Amongst  the  grandchildren  it  occurred  in  four 
on  both  sides,  in  four  on  one  side,  and  was  absent 
in  seven. 

Bronchial  asthma  and  hay  fever  form  a  closely 
associated  set  of  phenomena  which  are  clearly  inherited 
in  families,  and  have  their  basis  in  the  nervous  S3^stem. 
Hay  fever  is  a  slight  form  of  the  condition,  which  may 
develop  asthmatic  symptoms  under  special  irritation 
or  lowered  bodily  vitality,  and,  as  is  wtH  known, 
may  appear  or  disappear  in  an  apparently  capricious 
manner  at  different  ages  or  under  different  climatic 
conditions.  A  considerable  study  of  asthma  from 
the  clinical  and  inheritance  point  of  view  has  been 
made  by  Adkinson  (1920).  She  studied  400  cases, 
and  found  a  history  of  asthma  in  the  family  in  48  per 
cent,  of  the  cases.  Of  the  total,  191  were  sensitive 
to  proteins,  as  demonstrated  by  skin  tests,  while  the  re- 
maining 209  w^ere  negative  to  tests.  There  was  a  larger 
percentage  of  inherited  asthma  in  the  former  group. 

The  latter  t^^pe  or  ''  sensitive  asthma  "  is  more 
like  intensified  bronchitis.  Both  types  "  run  in 
families,"  and  both  usually  occur  in  different  members 
of  the  same  familv.  Asthma  is  found  to  be  inherited 
with  equal  frequency  through  either  parent.  Thirty- 
eight  family  histories  are  presented,  and  the  general 
conclusion  to  be  drawn  from  these  is  that  the  asth- 
matic tendency  is  inherited  as  a  Mendelian  recessive. 
Considering  individual  cases,  "  from  the  father's 
family  66  patients  ma}^  have  inherited  asthma, 
39  directly,  8  skipping  a  generation,  i  skipping  two 
generations,  and  18  collaterally.  From  the  mother's 
family,  64  patients  may  have  inherited  asthma, 
25  directly,  22  skipping  a  generation,  and  18  col- 
laterally." It  is  found  that  "  a  nearly  equal  number 
of  men  and  women  inherit  asthma  from  the  father, 
but   twice  as   many  women  as  men  inherit   asthma 


PHYSICAL  CHARACTERS  IN  MAN        139 

from    the    mother,    and    25    per    cent,    more    women 
than  men  inherit  asthma  directly  from  the  parents." 

It  is  concluded  (i)  that  where  both  parents  have 
asthma  or  hay  fever,  all  the  children  tend  to  show 
the  condition.  (2)  Where  one  parent  has  asthma 
and  one  is  normal  (seventeen  matings),  all  the  chil- 
dren (sixty)  were  normal.  (3)  When  one  parent  is 
asthmatic  and  one  normal,  but  probabl}'  carrying  the 
condition  (simplex),  then  equal  numbers  of  the  off- 
spring are  affected  or  unaffected  (sixt}^  asthmatic  and 
sixty-seven  normal).  (4)  When  both  parents  were 
normal,  but  could  be  shown  or  must  be  assumed 
to  be  carrying  the  condition  (simplex),  there  were 
three  times  as  many  asthmatic  as  normal  children. 
This  is  the  reverse  of  expectation.  It  is  partly  ex- 
plained by  incomplete  records  of  normals,  and  in  part 
by  the  addition  of  the  non-transmitting  type  of 
asthmatics.  But  it  is  at  least  possible  that  in  a 
character  of  this  kind,  in  the  cross  DR  x  DR  the 
recessive  character  is  able  to  express  itself  in  some 
instances  in  the  heteroz3^gous  condition.  Whether  this 
is  the  case  can  be  determined  from  further  evidence, but 
it  appears  probable  that  characters  may  depart  from 
strict  recessive  Mendelian  behaviour  in  this  respect. 

Reference  may  be  made  here  to  the  studies  of 
tuberculosis  by  Pearson  (1907)  and  Goring  (1909). 
They  compared  the  correlation  between  parent  and 
offspring  as  regards  the  incidence  of  the  disease  with 
that  between  husband  and  wnfe,  in  order  to  determine 
the  relative  importance  of  inheritance  and  infection 
in  the  development  of  this  disease.  Pearson  found  a 
correlation  of  0-5  between  parent  and  offspring,  which 
is  about  the  same  as  for  such  characters  as  eye  colour, 
height,  etc.,  indicating  the  same  tendency  to  in- 
heritance. Husband  and  wife,  on  the  other  hand, 
gave  a  correlation  of  0-24,  and  much  of  this  was  be- 
lieved to  be  due  to  assortative  mating.    Pearson's  data 


I40  HEREDITY  AND  EUGENICS 

were  taken  from  the  upper  classes.  Goring  studied 
British  convicts,  and  also  found  a  correlation  of  o-; 
for  parent  and  offspring,  but  none  for  husband  and 
wife. 

Wright  and  Lewis  (1921)  have  made  experiments 
on  guinea-pigs,  in  which  they  found  marked  differences 
in  resistance  to  tuberculosis  in  a  number  of  inbred 
families .  The  high  resistance  of  one  family  was  trans- 
mitted b}^  either  sex  to  the  offspring  in  crosses  with 
other  inbred  families.  It  is  found  that  the  factors 
determining  resistance  to  tubercle  are  not  closely 
related  to  the  other  elements  of  vigour,  such  as  growth- 
ratio,  adult  weight,  frequency  and  size  of  litter,  per- 
centage of  3'oung  born  alive,  and  percentage  of  young 
raised  to  weaning.  Inbreeding  brings  out  differences 
between  families  in  these  characters,  as  well  as 
independently  in  resistance  to  tuberculosis. 

Nothing  very  definite  appears  to  be  known  re- 
garding the  relation  of  cancer  to  inheritance  in  man. 
In  animals,  however,  many  definite  facts  have  been 
determined.  These  are  referred  to  by  L.  Loeb  (192 1). 
The  inheritance  of  specific  kinds  of  cancer  in  rats 
and  mice  and  other  animals  is  known — e.g.,  cancer  of 
the  inner  canthus*  of  the  eye  in  cattle,  cancer  of 
the  scrotum  in  rats,  and  sarcoma  of  the  thyroid 
in  rats.  Miss  Slve  has  shown  the  inheritance  of 
cancer  of  the  liver  and  other  special  forms  of  cancer 
in  certain  families  of  mice.  I  am  informed  that  the 
late  Professor  Plummer  recorded  cancer  in  three 
generations  of  wolves  in  the  Zoological  Gardens,  oc- 
curring always  in  the  same  place — viz.,  the  shoulder. 
In  the  fruit  fly,  Drosophila,  Stark  found  two  kinds 
of  inheritable  tumour-like  formations  originating  by 
mutation.  Others  have  since  been  found.  Since 
they  cause  death  they  are  classed  as  lethal  mutations. 
Loeb  concludes  that  the  endemic  occurrence  of  cancer 


* 


The  angle  next  the  nose  where  the  eyelids  meet. 


PHYSICAL  CHARACTERS  IX  MAN        141 

in  animals  is  due  to  hereditary  transmission  of  the 
disposition  to  cancer.  Infection  from  certain  para- 
sites may,  in  addition,  act  as  an  external  stimulus, 
comparable  with  Rontgen  rays. 

Probabl}^  in  principle  the  conditions  are  similar 
in  man.  Davenport  {191  8)  shows  that  the  tendency 
to  neurofibromatosis*  behaves  as  a  dominant  in 
heredity,  though  it  sometimes  skips  a  generation. 
It  is  a  rare  condition,  being  found  in  onh'  one  in 
2,000  cases.  Loeb  believes  that  in  man  probably 
one  or  more  factors  are  hereditarily  transmitted 
which  determine  the  intensity  of  the  tendenc}^  to- 
wards cancer  development.  In  many  cases,  cross- 
breeding appears  to  have  equalised  this  tendency  in 
man.  But  in  stationary  or  relatively  pure  popula- 
tions, as  in  parts  of  Norway,  there  is  evidence  of 
marked  differences  in  the  tendency  to  cancer  in 
different  strains  and  races. 

Stammering  is  due  to  an  unusual  excitability  or 
instability  of  cells  in  the  speech  centre  of  the  cerebral 
cortex.  The  tendency  to  stammer  is  clearly  inherited, 
although  it  not  infrequently  skips  a  generation. 
Bryant  (191 7),  who  has  examined  over  20,000  cases 
in  a  practice  extending  over  thirty-five  years,  states 
that  at  least  half  had  relatives  who  had  suffered  from 
some  nervous  speech  disorder.  The  condition  begins 
spontaneously  in  very  young  children  beginning  to 
speak.  A  case  is  cited  of  stammering  occurring  in 
four  generations,  but  no  other  pedigrees  are  given. 

The  Jewish  racialf  physiognomy',  which   has  been 

*  The  formation  of  numerous  tumours  from  necves,  and  con- 
taining connective  tissue. 

t  It  is  questionable  in  how  far  the  Jews  can  be  considered  a 
distinct  race.  Like  most  races,  they  have  had  a  mixed  origin, 
probably  from  Armenoid  and  Hamitic  stocks,  as  indicated  by  the 
presence  of  both  round  heads  and  long  heads  among  modern 
Jews.  The  fair  Jews  evidently  have  an  admixture  of  Nordic  blood. 
See  also  Salaman,  Trans.  Jewish  Hist.  Soc.  Eng.,  ix.  163,  1922. 


142  HEREDITY  AND  EUGENICS 

characteristic  for  over  2,000  3'ears,  is  believed  by 
Salaman  (191 1)  to  show  in  marriages  with  Gentiles 
incomplete  or  variable  dominance  and  segregation. 
Thus,  from  such  marriages  328  children  were  classed 
as  Gentile  in  facial  expression,  twenty-six  as  Jew, 
and  eight  intermediate.  The  subject  is  one  which 
invites  more  detailed  study.  Salaman  points  out 
two  other  inherited  peculiarities  of  the  Jewish  race: 
(i)  Amaurotic*  family  idioc}-,  a  disease  whose  victims 
die  in  earl}^  childhood,  and  which  is  known  onty  in 
Jews;  (2)  absence  of  alcoholism. 

As  our  knowledge  of  the  physiological  controls  of 
development  in  the  human  individual  increases,  a 
deeper  anatysis  of  man}^  physical  characters  will 
become  possible.  Various  abnormalities  in  man, 
such  as  brittle  bones  and  blue  sclerotics,t  are  already 
believed  to  be  due  to  an  hereditary  inferiority  of 
mesenchyme. J  And  the  glands  of  internal  secretion, 
such  as  the  pituitary,  pineal,  and  thyroid,  are  alread}^ 
known  to  control  growth  and  to  produce,  by  their 
presence  in  excess  or  defect,  various  characteristic 
conditions  of  the  features  or  the  limbs.  Inherited 
differences  in  these  glands  ma}'  thus  account  for  a 
whole  series  of  changes,  not  only  in  physical  con- 
formation, but  in  temperament  as  well.§ 

What  is  often  referred  to  as  a  remarkable  feature 
of  human  inheritance,  which  is  observed  also  and 
made  use  of  in  horse  and  cattle  breeding  (Hover, 
1 91 6),  is  the  occurrence  of  ''  prepotency."     Although 

*  Amaurosis  is  blindness  without  apparent  lesion  of  the  eye, 
resulting  from  disease  of  the  optic  nerve,  retina,  brain,  or  spine. 

J  The  hard,  white,  fibrous  membrane  forming  the  outer  coat 
of  the  eyeball,  except  at  the  front  where  it  is  replaced  by  the 
cornea. 

i  The  embryonic  connective  tissue,  which  forms  not  only 
connective  tissue,  but  also  the  bloodvessels  and  lymphatics. 

§  This  subject  will  be  referred  to  again  more  fully  later  (see 
pp.  210,  219). 


PHYSICAL  CHARACTERS  IX  MAN        143 

there  are  facts  which  bear  such  an  interpretation, 
prepotency  has  not  yet  received  a  satisfactory 
biological  explanation,  nor  is  it  clear  that  the  bio- 
logical facts  require  one.  Prepotency  is  believed  to 
be  increased  by  inbreeding,  and  differences  in  vigour 
or  energy  are  also  believed  to  be  involved  (Popenoe, 
1 91 6).  Mere  dominance  does  not  appear  to  be 
sufficient  to  explain  it,  and  the  interactions  of  factors 
may  be  concerned.  The  term  should  be  used  with 
great  care,  as  no  case  of  individual  prepotency  has 
yet  been  proved.  Perhaps  the  most  striking  case  in 
man  is  to  be  found  in  the  offspring  of  the  Mormon, 
Brigham  Young  (see  Journal  of  Heredity,  January, 
1 91 6).  In  a  photograph  of  some  eleven  of  his 
daughters  by  eight  different  wives  each  one  seems  to 
have  been  stamped,  as  it  were,  with  the  father's  own 
image,  though  the  resemblance  is  stronger  in  some 
cases  than  in  others,  but  the  characters  of  the  other 
parent  are  by  no  means  excluded.  The  resemblance 
is  particularly  striking  as  regards  the  strong,  firm 
mouth,  the  ears,  and  the  nose.  But  all  the  daughters 
are  said,  by  one  who  knew  the  family,  to  be  also 
musical,  amiable,  adaptable,  genuine,  sincere,  w^arm- 
hearted,  generous,  attractive,  magnetic  and  S3'm- 
pathetic,  and  temperamental  yet  reasonable.  More- 
over, all  were  good  mimics  and  excellent  cooks  and 
housewives,  having  also  their  father's  voice  and 
temperament .  This  remarkable  catalogue  of  qualities 
is  very  well  substantiated  by  an  accompanying 
photograph,  which  shows  a  group  of  motherl}-,  kind- 
hearted  women  with  remarkable  similarit}'  of  features, 
although  the  mother's  influence  is  also  clear  in  the 
differences  which  appear  between  half-sisters.  This 
resemblance  is  perpetuated  in  the  grandchildren, 
especially  the  girls,  and  may  be  partly  attributable 


to  assort ative  matmg. 


Another   question   of  heredity   which    I    have   not 


144  HEREDITY  AND  EUGENICS 

touched  upon  here  is  the  vexed  question  of  functional 
inheritance,  which  has  been  fully  discussed  by 
MacBride  (191  7),  and  has  been  considered  elsewhere 
(Gates,  1 921)  in  some  of  its  evolutionary  aspects. 
The  conceptions  of  Weismann  regarding  the  insula- 
tion of  the  germ  plasm  and  its  immunity  from  bodily 
and  environmental  influence  are  now  seen  to  have 
been  too  extreme.  Recent  experiments  of  Guyer 
and  Smith  (1920)  are  probably  of  significance  in  this 
connection.  B}^  injecting  into  fowls  a  finel}^  ground 
suspension  of  the  lenses  of  rabbits'  eyes,  the}'  ob- 
tained a  serum  from  the  fowl  which  was  then  injected 
hypodermically  into  pregnant  rabbits.  The  serum 
contained  a  cytolysin*  which  in  a  few  cases  more  or 
less  completely  dissolved  the  lenses  in  the  eyes  of  the 
embryo  rabbits,  although  those  of  the  mother  were 
unaffected.  Without  any  further  treatment  the 
condition  was  intensified  in  later  generations,  and 
was  inherited  through  the  male  as  well  as  the  female. 
If  these  results  were  actually  due  to  the  treatment, 
as  seems  highly  probable,  the}^  have  an  important 
bearing  on  the  question  of  functional  inheritance. 

*  A  substance  or  antibody  which  produces  dissolution  of  certain 
cells. 


CHAPTER  IV 

INHERITANCE  OF  MENTAL  CHARACTERS 

IN  MAN 

When    we    consider    mental    and    moral    traits,    the 

evidence  of  inheritance  in  many  cases  appears  sound 

and  beyond  dispute,  although  in  the  matter  of  human 

character  it  is  less  certain  how  far  the  accidents  of 

early  environment  ma}^  suppress  or  seriously  modif\' 

the    expression    of    various    inherited    traits.     Here 

we  are  in  a  region  where  the  structural  basis  of  the 

developed  inheritance  is  so  tenuous,  and  the  contact 

with  the  environment   so    intimate — character    and 

environment    becoming    so    mutually    involved    and 

interpenetrating — that  it  is  conceivable  that  the  laws 

applying  to  structural  characters  are  not  applicable 

with  the  same  rigidit}-  to   the  elements  or   methods 

of  reaction  that   go  to   make  what   we  call    human 

character.     Nevertheless,    critical    students    of    the 

subject  speak  with  one  voice,  and  it  is  quite  certain 

that  heredity  plays  an  equally  important  role  here 

also.     Indeed,  the  statistical  results  of  Pearson  (1904) 

indicate  that  for  siblings  the  intensit}'  of  resemblance 

is  as  great  for  mental  as  for  physical  traits.     He  chose 

eight  physical  characters — namel}^  health,  e3'e  colour, 

hair  colour,   curliness   of  hair,   cephalic  index,   head 

length,    auricular    height,    and    athletic   power — and 

eight  "  mental  "  characters:    vivacity,  assertiveness, 

introspection,  popularity,  conscientiousness,  temper, 

ability,    and    handwriting.     While     many    of    these 

characters    are    not     definite    enough    for    anything 

like   accurate   measurement,    and   therefore  have   no 

decisive    value,    yet    the    coefficient    of    correlation 

145  10 


146  HEREDITY  AND  EUGENICS 

between  brothers  and  sisters  (siblings)  comes  out 
0-51  for  physical  and  0-52  for  mental  characters. 
Schuster  and  Elderton  (1907),  from  a  statistical 
survey  of  Oxford  class  lists,  attempted  to  determine 
the  correlation  in  mental  ability  between  father  and 
son,  and  between  brothers  who  attended  the  Uni- 
versity. The}^  found  r=o-3i2  for  father  and  son, 
and  ^=0-405  for  brothers.  They  agree  with  Pearson 
that  mental  and  physical  characters  are  inherited 
with  the  same  intensity. 

.  Pearson  has  recently  (191 9)  considered  the  subject 
again  from  different  data,  comparing  the  results  of 
applying  the  Binet-Simon  test  (a)  to  children  in 
orphanages  in  California,  hence  under  nearty  uniform 
conditions ;  (b)  to  children  in  schools  of  Great 
Britain,  under  the  greatest  variety  of  conditions  of 
education  and  home  training.  Although  the  mental 
environment  w^as  relatively  uniform  in  one  set  of 
data  and  diversified  in  the  other,  yet  the  correlation 
of  intelligence  betw^een  siblings  w^as  the  same  in  both 
groups,  the  resemblance,  r =0-508  in  the  Californian 
and  r=0'5i5  in  the  English  data,  indicating  that 
heredit}'  and  not  environment  determined  the  differ- 
ences in  all  cases. 

But  the  situation  as  regards  some  ps3^chical  charac- 
teristics is  beyond  our  present  powders  of  accurate 
anal3^sis.  This  is  probably  because  we  have  not  yet 
learned  to  define  ps^^chic  characters  in  biological 
terms.  That  psychologists  are  beginning  to  recognise 
the  necessity  for  an  analysis  of  the  mind  from  the 
point  of  view  of  the  inheritance  of  mental  traits,  is 
shown  particularly  b}^  McDougall's  book.  Psychology, 
the  Study  of  Behaviour  {e.g.,  p.  187).  In  writing  of 
the  very  close  resemblances  in  intellect  and  character 
which  twins  often  show,  he  says :  "  The  more  children 
are  studied  from  this  point  of  view,  the  more  far- 
reaching  does  the  influence  of  heredity  appear."     At 


MENTAL  CHARACTERS  IN  MAN         147 

the  same  time,  he  finds  it  impossible  to  define,  except 
in  the  roughest  way,  the  innate  bases  of  these  heredi- 
tary pecuharities.  He  concludes  that  we  are  com- 
pelled to  believe  the}'  consist  in  "  inherited  mental 
structures  of  very  considerable  degrees  of  specialisa- 
tion." McDougall  points  out  that  biologists  and 
statisticians,  in  studying  the  inheritance  of  mental 
qualities,  have  frequently  used  crude  and  non- 
psychological  popular  distinctions,  such  as  good 
temper,  courage,  conscientiousness,  or  popularity, 
and  emphasises  the  need  for  accurate  psychological 
anal3'sis  of  the  constitution  of  the  mind  as  a  basis  for 
the  study  of  mental  inheritance.  Biologists  must 
undoubtedly  look  to  psychologists  for  aid  in  this 
direction.  In  speaking  of  ps3'chic  characters  we  are 
not  merely  referring  to  the  grosser  mental  differences, 
such  as  feeblemindedness  and  the  presence  or  absence 
of  musical,  mathematical,  or  general  ability,  whose 
inheritance  is  almost  universallv  admitted ;  but  to 
the  less  readil}'  definable  traits  which  go  to  make  up 
what  we  call  temperament,  disposition,  and  character. 
These  have  not  yet  received  adequate  biological 
classification,  treating  them  as  methods  of  reaction ; 
but  such  a  scheme,  combined  with  observations  and 
comparison  of  the  elements  of  human  characters, 
would  certainly  help  to  clarify  our  conceptions  con- 
cerning the  basis  of  the  differences  involved. 

May  it  not  be  also  that  in  individuals  who  are 
heterozygous  for  various  character  traits  which  are 
alternative  in  inheritance,  either  method  may  come 
into  expression  according  to  circumstances  ?  And 
since  every  individual  may  be  supposed  to  be  hetero- 
zygous for  many  pairs  of  traits  of  human  character, 
it  appears  possible  that  mental  traits  generally  difiVr 
from  structural  characters  in  that ,  in  the  former,  all  the 
alternative  possibilities  may  come  into  expression  in 
the  same  individual  at  different  times,  thus  adding  to 


148  HEREDITY  AND  EUGENICS 

the  complexit}^  of  the  result.  What  we  call  human 
character  in  its  developed  form  appears  to  consist 
in  the  acquired  habit  of  inhibiting  certain  inherited 
tendencies,  and  giving  free  expression  to  others. 
But  then,  again,  differences  in  powers  of  inhibition 
are  undoubtedly  inherited,  and  weakness  in  such 
powers  ma}^  lead  in  the  one  extreme  to  vicious 
tendencies,  and  in  the  other  to  a  free  expression  of 
the  other  elements  of  the  inheritance.  Nevertheless, 
there  is  always  a  choice  of  ideals  to  be  aimed  at, 
and  it  is  necessary  to  distinguish  in  conduct  between 
those  who  fail  to  reach  their  ideals  and  those  who 
deliberately  pursue  non-moral  ends. 

The  lay  mind  frequently  goes  astray  on  the  question 
of  the  inheritance  of  abilit}^  by  assuming  that  if  the 
sons  of  an  able  father  do  not  themselves  show  ability, 
this  is  a  case  of  "  failure  of  inheritance."  In  a 
scientific  view  of  inheritance  in  such  a  case,  one  of 
the  alternative  factors  has  been  inherited  instead  of 
that  which  conditions  ability — an  undesirable  instead 
of  a  desirable  quality  has  been  handed  on — or  at 
least  one  of  the  necessary  elements  for  the  expression 
of  abilit}'  is  missing.  In  types  of  ability  where  the 
correlated  action  of  several  independent  qualities 
or  factors  is  required,  the  appearance  of  the  same 
combination  of  exceptional  qualities  in  the  offspring  is 
very  likely  to  be  infrequent,  because  of  the  presence 
of  alternative  characters  in  the  germ  plasm. 

That  the  tendency  to  perform  certain  tricks  when 
in  a  particular  frame  of  mind  may  be  inherited,  was 
show^n  in  a  case  cited  by  Darwin  {Animals  and  Plants, 
chap,  xii.)  of  a  man  who,  as  a  bo}^,  had  the  habit, 
when  pleased,  "  of  rapidly  moving  his  fingers  parallel 
to  each  other,  and,  when  much  excited,  of  raising 
both  hands,  with  the  fingers  still  moving,  to  the  sides 
of  his  face  on  a  level  with  the  eyes."  As  a  grown 
man  the  trick  was  with  difficulty  suppressed,  but  one 


MENTAL  CHARACTERS  IX  MAX  149 

of  his  eight  children,  a  girl  of  four  and  a  half  years,  had 
exactly  the  same  trick.  Darwin  states  that  imitation 
was  out  of  the  question. 

Considering  now  the  inheritance  of  various  forms 
of  mentality,  Galton  (1869),  in  his  classical  work, 
Hereditary  Genius,  first  dealt  with  the  inheritance  of 
mathematical  and  various  other  forms  of  ability. 
This  and  the  subsequent  studies  are  too  well  known 
to  require  treatment  here.  Hurst  first  pointed  out  the 
probabilit}^  that  musical  ability  was  a  Mendelian 
recessive.  The  same  is  apparently  true  of  feeble- 
mindedness, at  least  in  its  extreme  form,  two  feeble- 
minded parents  almost  invariably  having  only  feeble- 
minded children.  The  exceptions  to  the  rule  are 
probably  explainable  by  illegitimacy.  The  literature 
of  feeblemindedness  is  too  well  known  and  too 
extensive  for  full  discussion,  but  reference  may  be 
made  to  some  of  the  results.  For  the  Mendelian 
interpretation  Goddart  (191 2,  1914)  and  Estabrook 
(191 6)  may  be  cited. 

Goddart  (191 4)  finds  that  at  least  50  per  cent,  of 
the  paupers  cared  for  in  American  institutions  are 
feebleminded,  and  at  least  50  per  cent,  of  the  pros- 
titutes are  estimated  to  be  in  the  same  condition. 
Many  criminals  come  in  the  same  class,  and  there  is 
also  a  close  relation  between  feeblemindedness  and 
alcoholism.  On  the  basis  of  graded  mental  tests  of 
the  Binet-Simon  Measuring  Scale  of  Intelligence,  in- 
dividuals are  classed  as  idiots  when  their  mental  age 
is  1-2  3^ears,  imbecile  when  it  is  3-7  3'ears,  and  morons 
when  it  is  8-12  years.  The  latter  would  be  called 
feebleminded  in  England.  The  mental  development 
may  stop  at  any  age,  and  feeblemindedness  is 
essentially  a  condition  of  early  suspension  of  mental 
development.  Various  accidents  and  certain  diseases 
in  childhood  may  result  in  feeblemindedness,  but 
it   would    appear    that    the  great    majorit}-  of    cases 


ISO  HEREDITY  AND  EUGENICS 

are  hereditary.  In  hereditar}^  feeblemindedness  the 
children  tend  to  have  about  the  same  grade  of 
mentality  as  the  parents.  Sometimes  accidents  in 
childhood  reduce  an  hereditary  moron  to  imbecility 
or  idioc}^  When  their  mentality  is  under  five  years, 
individuals  rarely  become  parents,  but  parenthood 
with  a  mental  age  of  seven  or  eight  is  common. 

The  careful  training  methods  of  the  Vineland  In- 
stitution show  that  it  is  impossible  to  develop  a  mind 
beyond  its  inherited  capacity.  The  mental  develop- 
ment may  stop  at  any  point,  and  training  cannot  push 
it  any  further,  although  the  most  patient  and  per- 
sistent efforts  have  evidently  been  made  in  this 
direction.  When  mental  progress  ceases,  it  is  neces- 
sary to  turn  to  manual  training  for  any  further 
development  of  the  individual. 

As  regards  inheritance,  Goddart  cites  42  matings, 
NF?  xFFc^ — i.e.,  a  heterozygous  but  normal  mother 
and  a  feebleminded  father — producing  144  children 
whose  mentality  is  known.  Of  these,  71  were  feeble- 
minded and  73  normal,  almost  exactly  in  accord  with 
the  Mendelian  expectation  of  equality.  On  the  other 
hand,  from  6  matings  FF  ?  xNFr?  there  were  193 
children  whose  mentality  is  known,  and  they  were 
122  feebleminded  to  71  normal.  Hence  it  appears 
that  the  number  of  feebleminded  considerabl}^  exceeds 
expectation  w^hen  the  mother  is  feebleminded.  Again, 
in  NFxNF  matings  (26)  there  were  185  offspring, 
and  the  mentalit}^  of  122  was  determined,  83  being 
normal  to  39  feebleminded  (expectation  for  one 
Mendelian  difference,  91 -5:  30-5).  Among  476  chil- 
dren from  FF  x  FF  matings,  only  6  are  recorded 
as  normal,  and  these  were  no  doubt  border-line  cases, 
or  perhaps  illegitimate.  Hence  the  evidence  clearl}- 
favours  the  interpretation  of  feebleinindedness  as  a 
simple  recessive. 

Holmes   (1921)   and  other  writers  are  less  willing 


MENTAL  CHARACTERS  IX  MAN 


I ;  I 


to  grant  this  conclusion.  Holmes  agrees  with 
Pearson  and  Heron  that  feeblemindedness  varies 
continuously,  but  he  admits  that  this  does  not 
imply  "  that  the  various  kinds  of  mental  defect  are 
not  transmitted  according  to  Mendel's  law."  He 
nevertheless  concludes  (p.  39),  ''  I  very  much  dcjubt 
if  the  facts  concerning  the  inheritance  of  mental 
defect  are  as  yet  known  with  sufficient  precision  to 
warrant  our  tr34ng  to  force  them  into  simple  Mendelian 
formulae."  We  cannot  agree  with  his  statement  that 
"  it  seems  improbable  a  priori  that  the  inheritance 
of  general  mental  development  would  follow  the 
simple  Mendelian  formula  for  the  inheritance  of  two 
contrasted  characters."  All  sorts  of  ph3^sical  defects 
in  man  and  other  animals,  and  in  plants,  are  known 
to  follow  the  behaviour  of  a  simple  recessive  character. 
This  appears  to  be  due  in  each  case  to  the  fact  that 
an  altered  element  (gene)  is  present  in  a  particular 
locus  of  a  chromosome,  and  we  find  no  difficult}'  in 
applying  the  same  view  to  mental  defects,  which  must 
have  a  physical  basis. 

We  may,  however,  point  out  an  inference  which 
follows,  and  has  not  yet  been  generall}^  recognised. 
If  feeblemindedness  is  inherited  as  a  ]\Iendelian 
recessive,  this  in  itself  furnishes  evidence  that  it  has 
arisen  as  a  defect  mutation  from  the  normal  con- 
dition. It  has  sometimes  been  suggested  that  feeble- 
mindedness represents  the  primitive  condition  of 
palseolithic  man,  which  has  persisted  in  certain  strains 
through  crossing  w^hile  the  gradual  mental  evolution 
of  the  remainder  of  mankind  has  continued.  If  the 
latter  h3'pothesis  were  true,  it  is  unlikely  that  simple 
alternative  inheritance  would  result.  On  the  whole, 
it  appears  most  likely  that  feeblemindedness  has 
arisen  many  times,  and  may  still  arise,  as  a  defect 
mutation  in  various  stocks,  although  the  condition 
itself    may   resemble    in    some   respects    the    mental 


152  HEREDITY  AND  EUGENICS 

condition  of  primitive  man.  Goddart  cites  a  family 
of  eleven  feebleminded  children  from  two  white  feeble- 
minded parents.  There  were  also  two  "  normal  " 
children,  but  they  were  black.  The  mentality  of 
the  negro  is  distinct  from  that  of  the  feebleminded. 
The  latter  presumably  occur  also  in  primitive  races. 
The  evidence,  so  far  as  it  goes,  also  appears  to  indi- 
cate the  gradual  evolution  of  the  mentality  of  normal 
civilised  man,  involving  man}'  steps,  whatever  may 
have  been  the  forces  involved. 

Holmes  points  out  that  where  a  normal  person 
married  to  a  feebleminded  one  has  some  feebleminded 
children,  it  is  too  easily  assumed  that  the  normal 
parent  was  heteroz3^gous  for  this  defect.  If  this  were 
always  true,  it  would  give  a  ver}-  high  frequency  for 
the  occurrence  of  this  latent  defect  (see  p.  159).  It 
seems  much  more  likely,  as  Holmes  points  out,  that 
the  normal  mentalit}^  show^s  variable  or  incomplete 
dominance,  especially  when,  as  is  usual  in  such 
matings,  the  normal  parent  is  also  intellectually 
below  par. 

Goddart  estimated  the  number  of  feebleminded 
in  the  United  States  at  300,000  to  400,000.  He 
thinks  it  important  that  the  public  should  understand 
the  mentality  of  a  moron  (mental  age  ten),  and  employ 
him  accordingl}',  recognising  his  limitations.  The 
moron  has  a  lifetime  in  which  to  learn  to  do  efficiently 
things  that  can  be  done  by  a  boy  of  ten.  Goddart 
suggests  that  their  training  should  be  carefully 
arranged  according  to  mental  age  tests,  that  as  many 
as  possible  should  be  "  colonised,"  some  sterilised,  but 
the  great  mass  "  educated  "  for  their  proper  work. 

The  *'  Mongolian  "  is  a  well-defined  type  of  mental 
defectiveness,  which  has  generall}'  been  regarded  as 
non-inherited.  The  oblique  eyes  and  round  faces  of 
Asiatics  are  combined  wath  short  stubb}'  fingers, 
rather    dry    rough    skin,    poor    circulation,    lack    of 


MENTAL  CHARACTERS  IX   MAN         153 

occipital  prominence,  and  usuall}'  in  older  cases  a 
deeply  furrowed  tongue.  The  mentality  is  nearly 
always  that  of  a  four-year-old  child.  Mongolians 
usually  appear  in  good-class  families,  they  are  not 
associated  with  feeblemindedness,  and  are  frequently 
the  last  born  in  large  families.  The}'  probably  result 
from  derangement  of  function  (uterine  exhaustion) 
leading  to  arrest  of  development,  beginning  at  a 
definite  point  in  the  prenatal  development.  The 
causation  of  the  type  according  to  Goddart  {191 4) 
appears  to  be  purely  physiological,  without  any 
element  of  inheritance.  Probably  defects  of  certain 
internal  secretions  are  involved.  It  has  recently  been 
claimed,  however,  that  there  is  some  reason  for 
regarding  Mongolianism  as  a  recessive  Mendelian  trait 
(see  Davenport,  1920).  There  is  evidence  also  that 
idiocy  frequent!}'  results  from  a  severe  infection, 
from  cerebro  -  spinal  meningitis,  or  from  S3'philis, 
alcoholism,  or  addiction  to  drugs  on  the  part  of 
the  parents.  But,  according  to  Davenport  (1920), 
statistics  show  that  the  great  mass  of  idiots  arise 
from  feebleminded  parents. 

The  controversy  between  the  schools  of  Pearson 
and  Davenport  turned  on  the  terms  in  which  the 
inheritance  of  feeblemindedness  is  to  be  stated. 
Both  agree  that  the  condition  is  inherited.  It  is 
possible  that  the  inheritance  is  not  always  strictly 
Mendelian,  although  it  appears  to  be  usually  in  con- 
formity with  the  simple  Mendelian  scheme.  It  would 
appear  that  occasional  departures  from  strict  con- 
formit}'  with  the  Mendelian  scheme  may  be  expected 
in  connection  with  the  inheritance  of  mental  charac- 
teristics. Nevertheless,  it  must  be  remembered  that 
with  feeblemindedness,  as  with  other  Mendelian 
characters,  the  expression  of  the  inheritance  may  be 
modified  by  the  presence  of  other  deternuners.  It  is 
also   possible   that    the   inheritance   follows    diflferent 


154  HEREDITY  AND  EUGENICS 

rules  in  certain  families,  as  is  known  to  be  the  case 
with  other  Mendelian  characters.  For  example,  if 
a  defect  has  arisen  in  an  ordinary  chromosome,  it  will 
be  inherited  probably  according  to  the  simple  scheme 
of  a  Mendelian  dominant  or  recessive,  but  if  it  has 
arisen  in  a  sex  chromosome  it  will  be  sex-linked. 

We  have  already  seen  that  feeblemindedness  is 
essentially  a  condition  of  arrested  mental  develop- 
ment. Epilepsy  is  a  closely  related  neuropathic  con- 
dition. Insanity  is  more  variable  in  its  causes,  and 
is  not  always  inheritable.  Many  data  on  the  inheri- 
tance of  mental  defects  are  given  by  Guyer  (191 6). 

The  relations  between  feeblemindedness  and  in- 
sanity have  frequently  been  misunderstood.     From 


^  ^'xD  "S^D        5^0        i)"^  D 

H  A'  .   r-l  A^  A.3      rJ^4      ^^r^6^7     16    ±9    1,0  ^,/ 


m    |-h/  X2  X3 

Fig.  29. — Hereditary  Imbecility  in  the  Female  Line. 

the  point  of  view  of  the  Binet-Simon  tests,  while 
feeblemindedness  gives  general  arrested  development 
at  a  certain  level,  insanity  and  epilepsy  show  ''  scat- 
tering "  in  the  tests — i.e.,  in  the  diseased  brain  some 
questions  in  various  years  will  be  missed.  ''  Scat- 
tering "  in  tests  of  the  feebleminded  indicates  the 
oncoming  of  insanity,  w^hich  may  not  become  evident 
for  several  years.  In  many  respects  feeblemindedness 
and  insanity  are  at  opposite  ends  of  the  mental  scale, 
although  an  unusually  high  percentage  of  feeble- 
minded become  insane.  Psychiatrists  maintain  that 
insanity  comes  in  highly  developed  nervous  systems, 
which  are  easily  thrown  into  an  abnormal  condition. 
Morons,  on  the  other  hand,  represent  often  a  vigorous 


MENTAL  CHARACTERS  IN  MAN         153 

organism  of  low  intellect  and  strong  physique.  They 
often  have  exceptional  strength,  but  cannot  show 
it  on  a  dynamometer  because  of  lack  of  will  power. 
They  represent  a  more  primitive  type,  with  dullness 
to  pain,  etc.,  but  under  exceptional  conditions  they 
may  perform  surprising  feats  of  strength. 

Sedgwick  (1861,  1863)  records  many  instances  of 
the  inheritance  of  insane  diatheses.  In  one  familv 
(Fig.  29)  hereditary  imbecility  appears  in  nearly 
all  the  females  of  two  generations,  while  the  sons 
were  normal.  No.  II.  3  was  eccentric  and  silly, 
while  No.  II.  11,  though  not  an  imbecile,  was  a 
religious  fanatic  and  became  a  Mormon. 

Inspection  of  charts  does  not  convince  one  that 
insanity  in  the  ancestry  has  any  potent  influence 
towards  causing  feeblemindedness.  On  the  other 
hand,  the  feebleminded  not  infrequently  have  insane 
offspring.  Insanity  is  a  symptom  of  nervous  de- 
rangement which  will  occasionally  give  rise  to  feeble- 
mindedness. Thus,  Goddart  cites  the  case  of  Nora  T., 
age  thirteen  years,  mentality  three.  Her  father  and 
mother  were  both  normal,  but  the  feeblemindedness 
in  the  father's  family  and  the  insanit}^  in  the  mother's 
family  apparently  brought  about  the  result  in  Nora. 
Again,  Bessie  X.  has  a  cousin  who  is  epileptic  and 
a  number  of  distant  relatives  who  are  insane  or 
epileptic,  while  others  are  "  queer  "or''  peculiar."  vShe 
is  fifteen,  with  a  mentality  of  two,  and  her  condition 
is  looked  upon  as  a  summing-up  of  various  morbid 
tendencies  which  have  appeared  sporadically  in 
several  generations  of  her  ancestors. 

It  is  worth  noting  that  the  drawings  of  animals 
by  the  feebleminded  sometimes  remind  one  in  style 
and  method  of  some  of  the  cave  drawings  of  early  man. 

While  feeblemindedness  is  certainl}'  far  removed 
from  genius  in  the  mental  scale,  representing  a 
primitive  undeveloped  mental  condition,  it   is  often 


156  HEREDITY  AND  EUGENICS 

but  a  step  from  insanity  to  genius.  Indeed,  many 
geniuses  would  pass  with  any  psychiatrist  as  true 
insanities.  The  diagnosis  may  depend  on  whether 
the  aberration  is  useful  or  dangerous.  But  it  is 
impossible  to  graft  genius  on  to  feeblemindedness,  and 
the  loss  of  a  whole  feebleminded  stock  would  not 
involve  the  suppression  of  a  single  genius.  For  in 
feebleminded  families  even  the  "  normals  "  are 
usually  of  low-grade  intelligence,  and  they  are  as  a 
rule  correspondingh'  low  in  social  grade.  Notwith- 
standing this,  it  is  clear  that  the  condition  of  the 
feebleminded  does  not  result  from  their  environment, 
but  rather  that  their  lack  of  capacity  causes  them  to 
gravitate  into  squalid  conditions,  since  the}-  cannot 
grapple  adequately  with  the  complexities  and  subtle- 
ties of  modern  civilised  life.  Urquhart  (1909) 
classifies  insanitv  as  melancholia,  mania  or  dementia 
which  are  acquired,  and  idioc}^  and  imbecility  which 
are  congenital.  The  latter  conditions  are,  usually 
at  least,  accompanied  by  gross  physical  deficiencies. 
The  pedigrees  of  insanity  are  usually  unsatisfactory 
in  failing  to  distinguish  betw^een  different  types,  and 
so  they  give  no  general  rule  of  inheritance,  although 
many  of  them  run  through  three  generations. 

Holmes  (1921)  has  pointed  out  that  the  germ  plasm 
of  neurotic  stocks  may  be  affected  in  a  variet}"  of 
wa^^s  in  different  individuals.  He  says  (p.  49): 
"  Charts  of  the  inheritance  of  insanity  show  that  the 
afflicted  individuals  exhibit  a  great  diversity  of 
symptoms  in  successive  generations."  Particular 
types  of  insanity,  however,  tend  to  run  in  certain 
families.  This  is  particularl}-  true  of  dementia 
prsecox  (see  p.  158)  and  periodical  insanity.  Unlike 
most  forms  of  insanity,  Huntingdon's  chorea*  appears 

*  Chronic  chorea  or  St.  Vitus'  dance  is  a  convulsive  nervous 
disease  with  irregular  movements,  dementia,  and  disturbance  of 
speech. 


MENTAL  CHARACTERS  IX  MAN         157 

to  be  usually  a  typical  dominant  character  in  in- 
heritance. While  the  feebleminded  may  be  con- 
sidered to  form  a  graded  series,  insanity  is  much 
more  varied  in  its  manifestations,  and  is  to  be  regarded 
as  a  pathological  condition  working  havoc  with  the 
normal  mental  mechanism,  rather  than  a  simple 
defect  of  mental  machiner}^  Some  types  of  insanity 
may  only  appear  late  in  life  and  yet  are  inherited, 
showing  that  the  seeds  of  ultimate  derangement  aru 
present  in  the  germ  plasm.  In  other  cases,  an 
exceptional  mental  or  physical  strain  may  bring  out 
phenomena  of  insanity  which  would  never  appear 
under  ordinary  circumstances. 

Ordahl  (191 9)  made  a  study  of  fifty  families  in 
California  containing  feeblemindedness.  He  con- 
cludes that  the  parents  of  the  feebleminded  are  often 
borderline  cases  and  escape  detection  by  ordinar}- 
means.  Seventy-two  per  cent,  of  the  fifty  families 
showed  defective  inheritance.  Of  the  living  children, 
5*6  per  cent,  were  idiots,  15-6  per  cent,  imbeciles, 
26-2  per  cent,  morons,  3-1  per  cent,  dull  normal, 
1-2  per  cent,  psychopathic,  48-1  per  cent,  normal. 
Ordahl  believes  that  the  moron  and  dull  normal  can  be 
detected  by  expert  means  in  the  earl}'  school  3'ears. 
Otis  (191 6)  aims  to  reconcile  the  views  of  Pearson  and 
Davenport.  He  considers  it  important  to  distinguish 
between  intelligence  and  "  brightness  " — i.e.,  the 
degree  the  child  is  in  advance  of  the  normal  develop- 
ment of  intelligence.  Pearson  showed  that  all  degrees 
of  intelligence  (meaning  brightness)  exist,  but  thi> 
does  not  exclude  the  Mendelian  inheritance  of  any 
degree  when  mated  with  feeblemindedness.  Otis 
concludes  that  "  the  existence  of  all  grades  of  bright- 
ness, and  the  possibility  of  the  universal  ]\Iendelian 
inheritance  of  different  grades  of  brightness,  arc- 
therefore  seen  to  be  entirely  compatible."  This  is  in 
accord  with  much  other  Mendelian  behaviour. 


158  HEREDITY  AND  EUGENICS 

A  mental  disorder  which  appears  to  be  confined  to 
Russian  Jews  (see  Davenport,  1920)  is  amaurotic 
famil}^  idioc}',  which  runs  in  famihes  and  appears  to 
be  a  simple  Mendelian  recessive.  Myoclonic  epilepsy 
(see  p.  108)  has  been  shown  by  the  extensive  pedigrees 
compiled  by  Lundborg  in  Sweden  to  be  inherited 
in  the  same  wa}'.  It  is  recognised  that  epilepsy  occurs 
in  a  great  variety  of  forms,  and  the  pedigrees  studied 
by  Davenport  and  Weeks  and  others  indicate  that 
the  common  form  at  any  rate  follows  the  same  rule 
of  inheritance.  A  relation  between  epilepsy  and 
feeblemindedness  is  also  indicated,  such  that  if  one 
parent  is  epileptic  and  the  other  feebleminded,  all 
the  children  will  be  either  epileptic  or  feebleminded. 
Various  investigations  indicate  (Davenport,  1920)  that 
dementia  praecox*  maybe  also  a  Mendelian  recessive. 
According  to  F.  W.  Mott  {Proc.  Roy.  Soc.  Med.,  June, 
1920),  this  condition  is  accompanied  by  a  complete 
arrest  of  spermatogenesis.  Riidin  (191 6)  finds  that 
various  other  psychoses  accompany  dementia  praecox, 
and  thinks  that  a  Mendelian  explanation  is  possible. 
Hoffman  (1921),  in  a  stud}'^  of  dementia  praecox  and 
the  manic  depressive  condition,  concludes  that  two 
factors  are  involved  in  the  former,  while  in  the  latter 
a  dominant  character  in  some  form  is  concerned. 
Siemens  (1921)  gives  a  list  of  inherited  abnormal 
physical  and  psychical  conditions. 

The  appalling  frequency  of  feeblemindedness  in 
some  parts  of  America  is  to  be  seen  from  statistics 
collected  (Sessions,  191 7)  in  one  county  in  Ohio, 
where  the  feebleminded  number  i  per  cent,  of  the 
population.  An  equal  frequenc}^  throughout  the 
State  of  Ohio  would  mean  47,000  feebleminded  within 
its  borders.  The  rapidity  with  which  the  problem 
is  becoming  still  more  serious  is  to  be  seen  from  the 

*  Adolescent  insanity  marked  by  melancholia  and  other 
emotional  states. 


MENTAL  CHARACTERS  IN  MAN         159 

fact  that  "  one  feebleminded  man  left  at  large  five 
generations  ago  is  responsible  for  seventy-five  feeble- 
minded persons  living  at  the  present  time."  The 
normal  population  of  the  country,  apart  from  immi- 
gration, can  hardly  have  increased  to  anything  like 
the  same  extent  during  this  time. 

But  even  if  all  feebleminded  individuals  were 
prevented  b}-  segregation  from  multiplying,  the  most 
difficult  part  of  the  process  of  eliminating  feeble- 
mindedness from  the  germ  plasm  of  the  population 
would  scarcety  have  begun.  For,  as  East  (191  7)  has 
pointed  out,  while  the  number  of  feebleminded  in  the 
whole  population  of  the  United  vStates  may  be 
estimated  at  3  per  1,000,  the  number  which  are 
carrying  feeblemindedness  as  a  recessive  defect  must 
be  nearer  i  in  14.  Punnett  (191  7)  puts  the  number 
even  higher,  and  emphasises  the  impossibihty  of 
greatly  reducing  feeblemindedness  in  the  population, 
except  by  segregating  also  those  who  are  carriers  of 
the  disease  as  a  recessive  quality.  He  shows  that  if 
the  proportion  of  the  feebleminded  in  the  United  States 
is  now  3  per  1,000,  then  it  would  require  250  genera- 
tions, or  about  8,000  years,  to  reduce  the  proportion 
to  I  in  100,000  b}-  the  method  of  merely  segregating 
or  sterilising  those  who  show  the  character.  It  is 
evident,  then,  that  the  elimination  from  reproduction 
of  those  showing  any  recessive  racial  defect  merely 
prevents  the  problem  from  becoming  more  serious, 
while  marked  improvement  in  the  germ  plasm  of  the 
population  can  only  be  effected  by  selection  against 
the  heterozygotes,  who  are  carrying  the  defect  in  half 
their  germ  cells.  More  accurate  mental  tests  ma>' 
make  it  possible  to  distinguish  such  heterozygous 
individuals  from  the  fully  normal  members  of  the 
population.  This  has  happened  in  the  history  of  the 
study  of  many  Mendelian  characters.  From  this 
point  of  view,  any  tendency  for  those  transmitting 


i6o  HEREDITY  AND  EUGENICS 

feeblemindedness  to  intermarry  will  have  the  desirable 
effect  of  bringing  it  to  the  surface  where  the  individual 
can  be  segregated,  rather  than  spreading  the  condition 
subterraneoush^  by  marriage  with  sound  stocks. 

That  even  the  most  degraded  family  is  not  entirely 
incapable  of  better  things  in  any  of  its  members  is 
shown  b}^  the  recent  histor}-  of  the  notorious  "  Juke  " 
family  (Estabrook,  191 6).  This  family,  whose  history 
has  been  a  continuous  record  of  crime,  vice,  and  feeble- 
mindedness, dates  from  1720-40,  and  has  been  an 
untold  burden  upon  the  State.  Dugdale  published 
a  histor}^  of  it  in  1877.  Estabrook  shows  that,  in  their 
history,  out  of  399  fertile  marriages  about  176  might 
be  classed  as  eugenic  matings  and  223  as  cacogenic. 
Fifty-five  per  cent,  of  these  matings  should  have  been 
prevented,  even  putting  the  eugenic  standard  as 
regards  intelligence  very  low.  Had  this  taken  place, 
the  remainder  would  now  show  less  than  5  per  cent, 
of  offspring  wdth  undesirable  traits.  In  fact,  over 
half  the  total  offspring  are  mentally  defective  or  have 
antisocial  traits.  The  occurrence  of  both  desirable 
and  undesirable  individuals  in  the  same  sibship  is 
often  startlingly  clear  in  these  families. 

Eugenic  studies  have  been  made  in  America  of  the 
Edwards,  Jukes,  and  Kallikak  families,  the  Hill  Folk 
and  the  Nam  family.  A  more  recent  study  of  a 
Pennsylvania  family  containing  good  and  bad  elements 
has  been  made  by  Miss  Key  (1920).  Two  pioneer 
families  of  German  descent  are  traced  through  five 
and  six  generations  on  American  soil.  They  mostly 
belong  to  the  great  middle  class,  containing  no 
eminent  members  and  no  notorious  criminals.  The 
study  began  with  four  young  feebleminded  in  a 
Pennsylvania  Institution.  The  history  of  this  family, 
with  a  network  of  descent  including  i  ,822  individuals, 
shows  the  establishment  of  lines  which  var}^  greatly 
in    social    efficiency.     Marriage    selection    has    given 


MENTAL  CHARACTERS  IX  MAX         i6i 

rise  to  three  strongl}^  contrasting;  lines,  the  original 
defects  persisting  or  becoming  accentuated  in  some 
hnes,  while  marriage  into  better  strains  has  produced 
other  hnes  socially  more  efficient.  One  famil\'  l)egan 
with  a  German  and  his  wife,  who  innnigrated  into 
Western  Pennsylvania  in  the  latter  part  of  the 
eighteenth  century.  He  was  a  fair  specimen  of  the 
pioneer  type,  but  his  wife  was  totally-  lacking  in  any 
sense  of  nuinber  or  quantity,  and  could  neither  sew, 
spin,  nor  w^eave  acceptably.  They  had  children, 
three  of  whom  were  apparently  feebleminded,  while 
the  others,  through  marriages  with  different  types, 
established  various  lines,  some  of  which  split  up  into 
divergent  branches.  Five  separate  strains  are  traced 
in  this  family.  Another  German  immigrant  and  his 
wife,  about  the  same  time,  had  twelve  children. 
They  were  very  tall  and  possessed  great  strength, 
qualities  which  some  of  their  descendants  perpetuated. 
Six  of  the  children  formed  socially  efficient  strains, 
four  died  without  marrying,  while  two  daughters, 
the  dullest  and  slowest  of  the  fraternitv,  but  with 
great  strength  and  endurance,  married  into  defective 
stock  belonging  to  the  previous  family,  and  gave  rise 
to  an  undesirable  strain. 

The  characteristics  of  the  various  lines  are  deter- 
mined by  the  combination  of  traits  carried  by  their 
founders,  together  with  the  leading  traits  of  the 
strains  into  which  they  married.  There  is  a  sifting 
out  in  every  generation.  Where  weakness  marries 
strength  the  defect  may  appear,  but  in  lessened  degree. 
This  results  in  the  practical  elimination  of  some 
defects  (in  their  external  expression),  and  in  increased 
efficiency.  The  intermarriages  of  defectives,  on  the 
other  hand,  give  a  continuous  line  of  defectives 
requiring  institutional  care.  Two  of  the  lines  con- 
tinue to  be  mixed,  showing  defectives,  degenerates, 
and  socially  fit.     The  degenerate  branches  gravitate 

II 


i62  HEREDITY  AND  EUGENICS 

downwards,  and  produce  nothing  but  degeneracy. 
The  rapid  multiphcation  of  these  people  is  most 
serious.  Miss  Ke}^  points  out  that  pubhc  opinion  is 
helpless  to  prevent  marriages  between  them,  and 
suggests  State  control  of  marriages  through  a  State 
Eugenics  Board,  with  power  to  prohibit  certain 
unions  under  penalty  after  studying  the  hereditar}' 
defects  of  the  proposed  parties  to  a  marriage.  But 
it  is  not  to  be  expected  that  a  ban  on  marriage  would 
prevent  people  of  this  type  from  reproducing  them- 
selves. It  is  noticeable  that  while  defective  members 
of  these  stocks  remain  for  the  most  part  within  a 
few  miles  of  their  place  of  origin,  and  hence  tend  to 
establish  a  defective  group  in  the  community,  the 
better  members,  by  marriage  or  otherwise,  remove  to 
greater  distances  and  a  new^  environment. 

Various  attempts  to  analyse  temperaments  and 
their  inheritance  have  been  made,  notabl}^  by 
Davenport  (191 5).  He  divides  temperaments  into 
h3^perkinetic  or  nervous  and  hypokinetic  or  phleg- 
matic, and  recognises  tw^o  grades  of  each.  A  dualism 
of  this  kind,  romantic  and  classic  types,  radical  and 
conservative,  feebly  and  strongly  inhibited,  he  finds 
running  through  the  whole  population ;  also  a  tendency 
for  matings  to  take  place  between  unhke  tempera- 
ments. He  hypothecates  a  factor  E  producing 
periodic  excitement,  its  absence  e  producing  calmness. 
Another  factor  C  makes  for  cheerfulness,  while  c 
permits  more  or  less  periodic  depression ;  and  he  finds 
that  C  and  E  are  independently  inherited.  As  a 
modern  attempt  in  the  anatomy  of  melancholy,  this 
shows  courage  in  the  effort  to  explore  a  field  which 
is  notoriously  full  of  pitfalls.  That  it  is  inadequate 
as  a  complete  analysis  appears  obvious.  The  desira- 
bility of  creating  ''  factors  "  for  calmness  and  cheer- 
fulness appears  very  doubtful. 

Nomadism,  or  the  wandering  instinct,  Davenport 


MENTAL  CHARACTERS  IN  MAN         163 

(191 5)  treats  as  a  fundamental  lunnan  instinct, 
which  is  typically  inhibited  in  intc^llii^cnt  civilised 
adults.  It  appears  to  be  a  sex-linked  recessive 
monoh3'brid  trait.  Sons  are  found  to  be  nomadic 
only  when  their  mothers  belong  to  nomadic  stock. 
Daughters  are  nomadic  only  when  the  mother  belongs 
to  such  a  stock  and  the  father  is  also  nomadic. 
The  impulse  occurs  frequently  in  families  showing 
such  periodic  behaviour  as  depression,  migraine,* 
epilepsy,  and  hysteria.  Nomadism  would  appear  to 
be  more  widespread  in  the  Anglo-Saxon  population 
of  North  America  than  in  the  resident  population  of 
Britain.  This  is  probably  because  emigration  has 
always  been  more  largely  of  the  roving  types,  the 
more  sedentary  elements  of  the  population  preferring 
to  remain  behind.  This  difference  probably  applies 
chiefly  to  the  labouring  and  agricultural  classes,  the 
higher  classes  being  able  to  satisfy  their  nomadic 
instincts  by  travel. 

The  relation  of  criminality  to  inheritance  is  often 
debated.  Obviously  it  cannot  be  a  simple  one. 
Davenport  (1920)  classifies  antisocial  behaviour  as 
due  to  one  of  the  following  four  sets  of  conditions : 
(i)  Ignorance  of  the  mores  (or  social  requirements), 
merely  through  lack  of  opportunity  to  learn  the 
mores.  This  condition  would  apply  partially  to  the 
foreigner,  or  to  the  improperly  or  insufficiently  taught 
offender.  (2)  Ignorance  of  the  mores  through  lack 
of  capacity  to  understand  what  society  expects. 
This  is  characteristic  of  the  feebleminded.  (3)  Know- 
ledge of  the  mores,  accompanied  by  a  social  blindness 
and  inability  to  have  the  action  controlled  b}'  a 
knowledge  of  w^hat  society  expects  of  one,  because 
of   lack   of  gregarious,   social,   or   altruistic    instinct. 

*  A  nervous  affection  marked  by  periodic  headache,  often 
confined  to  one  side  of  the  head,  and  accompanied  by  nausea 
and  other  symptoms. 


1 64  HEREDITY  AND  EUGENICS 

Here  belong  the  extreme  individualists  and  anarchists. 
(4)  Knowledge  of  the  mores  with  presence  of  the 
social  instincts,  but  with  inability  to  meet  the  ex- 
pectations of  society  through  insufficient  inhibition 
or  self-control.  This  insufficiency  may  be  general 
and  permanent,  or  it  may  be  temporary  (periodic). 
This  would  include  the  hyperkinetic,  the  hysterical 
and  epileptoid  offenders.  It  is  thus  evident  that 
a  tendency  to  the  inheritance  of  criminality  will  vary 
according  to  its  type. 

Another  work  by  the  same  author  (191 9),  on 
heredit}^  in  naval  officers,  contains  genealogical  and 
biographical  data  of  many  English  and  American 
naval  officers,  including  Raleigh,  Hardy,  and 
Nelson.  Its  attempt  to  treat  thalassophilia,  or  love 
of  the  sea,  as  an  inherited  trait  is  not  very  happy 
as  a  means  of  analysing  the  inheritance  of  men  who 
were,  in  many  cases,  remarkably  diverse  in  their 
exceptional  qualities.  The  Mendelian  conception  is 
valuable  in  connection  with  so  many  human  traits, 
that  it  w^ould  be  unfortunate  if  any  loose  and  un- 
justified usage  of  it,  as  in  the  present  instance,  with- 
out any  adequate  understanding  of  the  nature  of 
the  differences  involved,  should  have  the  effect  of 
throwing  doubt  on  the  man}^  cases,  mental  as  well 
as  physical,  of  Mendelian  inheritance  in  man.  It 
is  clearly  a  matter  of  greater  difficulty  to  prove 
the  Mendelian  inheritance  of  a  mental  than  of  a 
physical  trait,  and  correspondingly  increased  caution 
is  necessary. 

A  very  good  summar}''  of  the  general  arguments  in 
proof  of  the  inheritance  of  mental  traits  is  given  by 
Popenoe  (191 6).  Failure  to  recognise  the  fact  of 
mental  inheritance  comes  largely,  now,  from  certain 
psychologists  and  educationists  whose  biological 
ignorance  and  lack  of  understanding  of  heredity  are 
a    matter    for    commiseration.     Many    psychologists, 


MENTAL  CHARACTERS  IX  MAX         165 

however,  now  clearly  recognise  the  inheritance  of 
mental  traits.  That  mental  traits  are  inherited  in 
animals  has  been  clearly  shown  in  one  case  by  Castle, 
who  proved  that  in  crosses  between  wild  and  tame 
rats  wildness  is  transmitted  by  the  father  to  offspring 
who  have  never  .seen  their  father  or  had  experience 
of  any  behaviour  but  that  of  their  tame  mother. 
Those  who  deal  with  psychological  tests  of  such 
animals  as  rats  and  mice  soon  learn  to  recognise 
individual  differences  in  psychology  which  make 
the  simple  tests  of  efficiency,  such  as  maze-running, 
appear  entirely  inadequate  unless  careful  allowance 
is  made  for  such  temperamental  differences. 

Modern  psychology  has  developed  in  two  directions, 
which  tend  to  make  it  more  biological  and  are  of 
interest  in  connection  with  the  present  discussion : 
(i)  The  theories  of  Freud  and  Jung  dealing  with  the 
formation  of  mental  complexes,  unconscious  sup- 
pression, mental  conflicts,  etc.,  and  tending  to  show 
that  mental  experiences  very  early  in  life,  and  quite 
unperceived  at  the  time,  ma}^  have  a  profound  in- 
fluence on  the  later  mental  development  ;  (2)  be- 
haviourism, which  has  grown  out  of  the  purety 
zoological  experimental  study  of  animal  behaviour, 
from  protozoa  to  the  anthropoid  apes.  The  second 
phase  need  not  particularly  concern  us  here.  Avery 
good  summary  of  the  Freudian  phase  has  been  written 
by  Tansley  (1920).  Instead  of  man  being  the  rational, 
thinking  being  the  older  psychology  pictured  him, 
his  mentality  is  seen  to  be  built  up  on  a  mass  of 
instincts  inherited  from  his  animal  ancestry,  giving 
him  tendencies  or  instincts  which  constantly  require 
to  be  altered  or  repressed  under  the  conditions  of 
civilised  life.  When  not  repressed,  he  acts  first,  and 
rationalises  his  action  afterwards.  This  repression, 
often  unconscious,  ma}'  lead  to  subconscious  mental 
conflicts  and  other  difficulties.     Kempf  (1921)  shows 


i66  HEREDITY  AND  EUGENICS 

how  the  bodily  functions  have  their  effect  on  the 
mind,  and  an\^  defect  is  unconsciously  compensated 
for  b}^  the  individual.  This  may  ultimately  lead  to 
a  pathological  condition  of  the  mind,  in  other  words, 
insanity,  particularly  in  a  time  of  mental  stress, 
and  under  some  conditions  a  psychoanalysis  may 
restore  the  mental  balance.  The  development  of 
insanity  is  thus  closely  wrapped  up  with  bodily  con- 
ditions. That  there  is  also  an  element  of  inheritance 
in  man}^  cases  of  insanit}-  is  undeniable,  but  it  remains 
to  be  determined  precisely  what  that  element  is  in 
different  cases.  The  situation  is  obscure  in  com- 
parison with  feeblemindedness  where  the  nature  of 
the  inheritance  is  clear.  Insanities  also  show  a 
greater  variety  of  types,  and  they  cannot  be  graded 
in  a  simple  series  like  the  mental-age  series  of  the 
feebleminded.  The  compelling  force  of  the  excessive 
development  or  derangement  of  some  autonomic 
bodily  function  will  usually  furnish  the  immediate 
cause  of  an  insane  manifestation.  Various  inherited 
derangements  of  the  nervous  control  of  the  bod}' 
may  then  provide  the  basis  for  the  development  of  an 
insane  diathesis. 

Inherited  mental  differences,  no  doubt,  go  back 
to  germinal  changes  affecting  the  nervous  system. 
Traced  backwards  in  the  ontogeny,  they  must  have 
a  purety  physical  basis  like  other  germinal  changes.* 
The  description  of  a  breed  of  goats  in  Kentucky 
(Hooper,  191 6)  is  instructive  in  this  connection. 
When  frightened,  their  forelegs  become  stiff,  and 
they  hop  along,  dragging  their  hind  legs.  If  much 
frightened,  the  latter  also  become  stiff,  and  the  animal 
falls  over.  Such  a  breed  must  have  arisen  through  a 
germinal  change  affecting  chiefly  the  nervous  system. 

*  Yerkes  has  shown  that  in  crosses  between  wild  and  tame  rats 
wildness  will  appear  in  the  offspring  even  when  the  father  was 
wild  and  the  young  were  reared  by  tame  mothers. 


MENTAL  CHARACTERS  IN  MAN         167 

A  very  similar  condition  appears  in  sheep,  and  also 
in  horses  and  cattle,  as  a  result  of  feeding  too  freely 
on  pampas  grass,  Poa  argentina  (Jones  and  Arnold, 
191 7).  But  it  is  a  form  of  intoxication,  and  is  not 
inherited.  Cole  (1920)  describes  in  guinea-pigs  a 
form  of  congenital  palsy  which  is  not  exactly  like 
any  nervous  disorder  in  man,  though  it  resembles 
ataxia  in  pigeons,  which  Riddle  finds  is  a  recessive 
character  with  some  irregularities  in  inheritance. 
Congenital  palsy  in  guinea-pigs  runs  a  brief  course, 
ending  in  death  at  an  early  age.  The  neurosis 
appeared  in  191 4,  and  is  characterised  by  clonic 
spasms,*  particularly  of  the  legs,  in  which  the  animal 
lies  helpless.  It  is  inherited  as  a  simple  Mendelian 
recessive,  heterozygotes  being  entirely  normal. 
Hurst  states  that  ''  feeblemindedness  "  in  pigeons  is 
a  recessive.  Tumbling  in  pigeons  and  *'  waltzing  "  in 
inice  and  rats  (again  recessive)  are  other  examples 
of  inherited  nervous  disorders  in  animals.  These 
defects  have  been  shown  to  be  due  to  defective 
semicircular  canals. 

The  inheritance  of  wildness  in  rats  has  been  referred 
to  elsewhere.  Yerkes  (191 3)  made  a  study  of  wild 
and  tame  rats  and  their  Fi  and  Y^  hybrids.  He 
proved  that  wildness,  savageness,  and  timidity  are 
inherited,  although  wildness  and  timidit}'  are  very 
difficult  to  distinguish.  Coburn  (1922)  has  made  a 
study  of  1,300  mice,  hybrids  between  wild  and  tame, 
in  three  generations.  He  made  careful  psychological 
tests  of  his  animals,  and  concludes  that  the  in- 
heritance of  wildness  and  savageness  in  mice  is 
Mendelian  of  the  "  blending  "  or  multiple  factor  type, 
but  much  more  work  is  needed  before  the  precise 
manner  of  inheritance  can  be  stated.  He  thinks, 
however,  that  the  two  behaviour  complexes,  wild- 
ness   and    savageness,    result    from    several    different 

*  Spasms  in  which  rigidity  and  relaxation  succeed  each  other. 


i68  HEREDITY  AND  EUGENICS 

inheritance  factors  which  appear  to  follow  Mendelian 
rules. 

Modern  psychology  is  only  beginning  to  recognise 
the  importance  of  the  inheritance  element  in  mental 
differences .  McDougall  ( 1 9 1 9)  clearly  recognises  such 
an  element  in  inheritance,  but  many  psychologists 
are  still  too  engrossed  with  the  mind  itself  to  recognise 
the  genetic  relationships  of  its  various  elements  to 
the  minds  of  relatives.  Psychopathologists  also 
frequently  fail  to  appreciate  that  any  element  of 
mental  inheritance  exists.  For  example,  Kempf 
(1921)  studies  the  development  of  the  mind  with  a 
complete  disregard  of  the  facts  of  mental  inheritance. 
He  devotes  forty  pages  to  an  analysis  of  Darwin's 
mental  development  from  the  psychoanalytical  point 
of  view.  We  hear  nothing  at  all  of  the  inheritance 
of  mental  traits,  but  everything  is  explained  on  the 
basis  of  the  mental  relationships  between  Charles 
Darwin  and  his  father,  the  early  influence  of  his 
mother  (who  died  when  he  was  eight  years  of  age), 
and  afterwards  of  his  wife.  He  sees  in  Darwin's 
mother's  "  charming  interest  in  nature,"  her 
"  romantic  fondness  for  flowers,"  her  keeping  of 
pigeons,  and  her  interest  in  the  theories  of  her  father- 
in-law,  Erasmus  Darwin  (author  of  Zoonomia),  a 
basis  for  Darwin's  interest  in  nature.  This  inspired 
her  son  to  search  for  ''  the  secret  of  her  fascination." 
At  the  age  of  eight  he  had  alread}^  begun  to  collect 
"  all  sorts  of  things."  The  writer  mentions  that 
collecting  was  a  characteristic  of  several  of  Darwin's 
uncles,  but  fails  to  recognise  any  element  of  in- 
heritance in  the  reappearance  of  this  trait.  It  seems 
more  probable  that  Darwin  inherited  this  quality, 
than  that  it  was  based  on  the  development  of  a 
childish  fantasy  which  originated  through  his  mother's 
influence  on  his  early  mental  development. 

Granting  that   Darwin's   mother's   ''  charming  in- 


MENTAL  CHARACTERS  IN  MAN         169 

terest  in  nature  "  was  a  fact,  this  interest  may  have 
been  a  portion  of  her  son's  inheritance.  Kempf 
(p.  216)  impUes  that  the  mother  had  unconsciously 
''  named  her  wish  for  her  boy's  destiny,"  and  that 
this  early  attachment  to  his  mother  had  influenced 
the  whole  course  of  his  life,  preventing  him  from 
following  his  father's  and  grandfather's  profession 
of  a  physician.  But  Darwin's  attachment  to  his 
father,  who  survived  to  influence  him  throughout  his 
development,  seems  to  have  been  equally  strong. 
It  seems,  at  least,  very  unlikely  that  Darwin's  mother- 
attachment  was  the  basis  of  his  attraction  to  natural 
histor\^.  Rather  his  taste  for  natural  history  appears 
to  have  represented  the  inevitable  expression  of  an 
inherited  tendenc}^  a  tendency  which  finally  overcame 
all  obstacles  and  found  an  environment  (the  Beagle 
voyage)  where  it  could  develop  freely.  There  are 
many  similar  instances  of  exceptional  men  whose 
development  necessitated  the  overcoming  of  parental 
wishes.  The  recognition  of  Darwin's  inheritance, 
which  made  his  greatness  possible,  does  not  lessen 
the  importance  of  parental  attachment  as  a  guide 
in  development,  or  in  some  cases  a  hindrance  if 
unwisely  exercised. 

Kempf  goes  on  to  consider  Darwin's  later  chronic 
ill-health.  He  thinks  Darwin  suffered  from  an 
''  anxiety  neurosis,  due  to  consistent  affective  sup- 
pression," from  anticipation  of  what  his  work  would 
mean  to  civilisation,  the  criticisms  and  opposition  it 
would  arouse.  Although  Darwin  suffered  from  sea- 
sickness and  dizziness  during  the  voyage,  yet  his  first 
experience  of  becoming  "  unwell  "  was  after  his 
return,  and  in  his  early  life  he  was  very  vigorous  and 
fond  of  sports.  "  The  later  course  of  his  anxiety 
indicates  that  it  was  a  reaction  to  his  efforts  to  adjust 
himself  to  his  career,  his  father  (who  had  opposed  the 
voyage  on  the  Beagle,  and  wished  him  to  take  up 


I70  HEREDITY  AND  EUGENICS 

a  church  career  after  his  failure  to  be  interested 
in  medicine,  and  on  whom  he  was  economically 
dependent),  and  his  mating."  The  necessity  for 
avoiding  conflicts  in  order  not  to  be  distracted  from 
his  researches  was  another  element  in  his  adjustment. 
Of  course,  Darwin's  ill-health  has  been  much  written 
about.  This  brief  account  is  given  as  a  typical 
example  of  the  psychoanalytic  method  applied  to  a 
man  of  genius.  It  w^ould  gain  greatly  in  value  if  it 
recognised  the  importance  of  inheritance  as  furnishing 
the  potentialities  on  which  environmental  influences 
play.  It  ought  to  be  obvious  that  if  Darwin  had  been 
a  person  of  mediocre  abilit}^,  neither  his  mother 
attachment  nor  anything  else  could  make  of  him  a 
great  naturahst.  It  is  this  fact  which  the  psycholo- 
gist too  often  overlooks. 

As  regards  the  inheritance  of  mental  aptitudes,  that 
musical  ability  "  runs  in  families,"  and  is  more 
frequent  in  some  races  than  in  others,  is  well  known. 
Not  onty  is  this  true  of  such  groups  as  the  Bach 
family,  but  also  of  innumerable  other  families  of  less 
exceptional  musical  ability.  Hurst  first  suggested 
that  this  characteristic  w^as  a  Mendelian  recessive. 
A  study  of  five  musical  families  by  Drinkwater  (191 6) 
partly  supports  this  conclusion.  A  family  of  organists 
was  traced  through  several  generations,  and  in  every 
case  where  both  parents  were  musical  all  the  children 
showed  musical  ability.  In  another  branch  of  this 
family,  where  both  parents  lack  musical  ability,  all 
the  children  lack  it.  These  families  w^ere  united  by 
marriage,  but  instead  of  all  the  children  being  non- 
musical,  exactly  50  per  cent,  of  them  w^ere  musical, 
two  being  professionals  of  great  abilit}-.  It  therefore 
appears  that  musical  ability  may  be  a  recessive  w^hich 
may  nevertheless  appear  in  some  cases  in  the 
heteroz^^gous  condition.  Artistic  abilit}^  was  also 
traced     through    four    generations    as    a    recessive 


MENTAL  CHARACTERS  IN  MAN         171 

character.  But  further  evidence  is  required  for 
clear  conclusions  regarding  the  inheritance  of  musical 
and  artistic  ability. 

Miss  Stanton  (1922)  has  made  records  of  the 
musical  capacities  in  various  American  families  con- 
taining one  or  more  distinguished  musicians.  The 
measures  of  musical  capacity  used  were  (i)  sense  of 
pitch,  (2)  sense  of  intensity,  (3)  sense  of  time,  (4)  tonal 
memory.  These  are  believed  from  extensive  experi- 
mentation to  be  basic  qualities  in  connection  with 
musical  ability,  being  little  affected  by  practice,  age, 
musical  training,  sex,  or  general  intelligence.  Dis- 
crimination tests  were  made  on  the  basis  of  phono- 
graphic records  and  standard  laboratory  apparatus, 
531  individuals  being  classed  as  poor,  average, 
superior,  etc.,  on  the  basis  of  each  test.  As  regards 
inheritance,  the  results  are  not  extensive  enough  to 
warrant  any  very  definite  statement  of  laws.  It  is 
nevertheless  suggested  that  the  data  indicate  the 
dominance  and  segregation  of  superior  capacity  from 
average  and  poor  capacities.  It  is  concluded  that 
"  the  inheritance  of  musical  capacities  seems,  indeed, 
to  follow  Mendelian  principles,  but  the  method  of 
inheritance  is  so  complex  that  it  is  impossible  now  to 
state  how  many  factors  may  be  present."  It  is 
doubtful  if  such  a  result  has  much  value,  beyond  the 
recognition  of  the  fact  that  degrees  of  musical  capacity 
are  probably  inherited. 

Pearson  treats  handwriting  as  a  mental  charac- 
teristic. There  is  no  doubt  that  it  is  an  extraordinary 
index  of  human  character,*  and  can  be  used  for  an 
intimate  analysis  of  the  character  by  one  who  is 
expert  in  the  comparison  and  analysis  of  different 
types  of  cheirograph3^  There  is  nothing  mystical 
in    this    relationship.     The    handwriting    is    an    ex- 

*  This  statement  has  often  been  disputed,  but  from  personal 
experience  I  am  convinced  that  it  is  a  fact.     See  also  p.  172. 


172 


HEREDITY  AND  EUGENICS 


pression  of  one's  manner  of  doing  things.  It  may  be 
neat  or  slovenly,  run  together  or  disconnected,  large 
and  sho\\y  or  small  and  carefulh^  formed,  with  long 
loops,  precisely  crossed  t's,  large  capitals,  long 
flourishes,  etc.  In  the  hands  of  an  expert  these,  and 
many  much  more  minute  details,  yield  a  remarkably 
accurate  analysis  of  the  character  and  capacities  of 
the  individual.  The  autograph  is  truly  the  product 
of  the  whole  man.  If  you  write  another  man's  name 
you  will  write  it  differently  from  his  autograph,  unless 
your  characters  reseinble  each  other,  in  w^hich  case 
3^ou  ma}^  form  the  letters  in  a  very  similar  way. 
There  is  one  man  whose  name  I  write  almost  exactly 
as  he  does,  and  I  know  that  our  characters  have  many 
points  of  resemblance. 

The  anatysis  of  this  relationship  between  character 
and  handwriting,  a  relationship  which  extends  to  the 
minutest  details,  is  worthy  of  scientific  study.  I 
know  of  one  woman,  a  teacher,  who  is  almost  in- 
fallible in  delineating  the  character  of  any  person 
whom  she  has  never  seen,  from  only  a  few  lines  of  the 
handwTiting.  It  seems  to  be  a  matter  of  sensing  the 
significance  of  different  t3^pes  of  curves  and  various 
other  features  of  handwriting,  as  they  blend  together 
in  the  expression  of  the  character  of  the  individual. 
The  mood  of  the  individual,  whether  elated  or  suffering 
from  depression,  is  also  registered  in  the  hand- 
writing. Indeed,  the  method  is  so  accurate  that 
specimens  of  the  handwriting  could  undoubtedly  be 
used  to  determine  the  character-traits  of  deceased 
persons  concerning  w^hom  insufficient  evidence  is 
available  in  the  study  of  mental  inheritance.  The 
striking  resemblances  one  sometimes  sees  in  the  hand- 
writing of  relatives  is  associated  with  inherited 
similarities  in  character.  Identical  twins,  however, 
sometimes  show  fairl}^  marked  differences  in  hand- 
WTiting.     This  subject  of  the  handwriting    of   twins 


MENTAL  CHARACTERS  IN  MAN         173 

is  worth}'  of  further  investigation.  It  should  throw 
hght  on  (1)  the  similarities  between  twins;  (2)  the 
limits  of  relation  between  handwriting  and  character. 

Another  important  fact  which  the  student  of 
eugenics  must  needs  bear  in  mind  is  not  only  that  a 
vast  array  of  biological  character-differences  exist, 
which  are  being  reshuffled  from  generation  to 
generation,  but  that  in  the  individual  the  greater 
number  of  these  characters  will  be  in  the  heterozygous 
or  hybrid  {i.e.,  inconstant  or  splitting)  condition. 
This  has  both  advantages  and  disadvantages  from 
the  point  of  view  of  selective  mating  and  offspring. 
Among  the  advantages  may  be  reckoned  the  fact 
that  the  offspring  are  sure  to  show  a  variet}^  of  mental 
and  physical  characteristics — i.e.,  to  differ  markedly 
from  each  other  (except  in  the  case  of  identical  twins) ; 
while  the  disadvantage  is  measured  by  the  number  of 
unfavourable  recessive  characters  carried  bv  both 
parents.  The  fact  that  both  parents  may  be  carrying 
some  of  the  same  unfavourable  or  deleterious  recessive 
characters  is  the  chief  and  probably  the  only  sound 
biological  argument  against  cousin  marriages.  Here  it 
may  be  pointed  out,  that  w^hile  it  is  impossible  to  know 
with  certainty  from  a  human  pedigree  all  the  recessive 
characters  which  are  carried  by  an  individual,  yet  it 
will  be  possible  to  determine  some  of  them  from  a  study 
of  the  ancestors,  and  particularly  of  the  collateral 
lines,  such  as  uncles  and  cousins  and  their  families. 

Eugenic  action  should,  then,  be  based  upon  four 
separate  factors:  (i)  Positive  selection  for  desirable 
qualities,  w^hich  are  frequently  dominant ;  (2)  negative 
selection  against  undesirable  recessive  qualities  which 
appear  in  collateral  or  ancestral  lines,  and  may 
therefore  be  carried  in  the  family  germ  plasm ; 
(3)  isolation  of  individuals  having  undesirable 
dominant  qualities ;  (4)  correlated  with  this  should  be 
an    effort    to    foster     matings    between    individuals 


174 


HEREDITY  AND  EUGENICS 


showing  the  same  desirable  recessive  quahty.  All 
this  implies  an  array  of  information  more  elaborate 
than  anyone  possesses  concerning  his  own  ancestors 
and  more  distant  relatives,  unless  he  has  made 
exceptional  efforts  to  collect  and  compile  the  necessar^^ 
data  from  ancestral  records,  portraits,  and  other 
sources.  It  w^ill  also  be  understood  that  although 
I  have  here  spoken  of  dominant  and  recessive 
characters  as  though  the  difference  betw^een  them 
were  absolute,  yet  it  is  well  known  that  in  many 
instances  this  is  not  really  the  case.  It  is  quite  likely 
that  in  man  the  interrelations  with  other  germinal 
qualities  may  bring  about  variable  dominance;  and 
the  heterozygous  combination  of  a  pair  of  characters 
much  more  often  gives  an  intermediate  result,  or  at 
least  one  in  which  the  recessive  exhibits  some  tangible 
effect  of  its  presence.  Even  in  the  case  of  such 
abnormalities  as  brachydactyly,  which  are  commonly 
treated  as  dominants,  there  is  some  evidence  that  the 
homozygous  condition  of  the  abnormality  is  much  more 
extreme,  and  indeed  non-viable  (see  p.  90).  If  this  is  the 
case,  it  shows  incidentally  that  the  original  mutation 
must  have  been  itself  heterozygous.  It  also  follows 
that  the  heterozygous  condition  is  intermediate  be- 
tween the  normal  and  the  homozygous  condition  of 
the  abnormality,  although  the  latter  is  non-viable 
and  cannot  reach  mature  development.  Abnormali- 
ties in  which  the  heteroz3^gous  condition  alone  exists, 
since  the  homozygous  is  non-viable,  are  not  perhaps  in 
the  strict  sense  dominants,  although  they  are  usually 
referred  to  as  such.  Factors  which  can  only  bring 
about  development  when  in  the  heteroz^^gous  con- 
dition are  one  t3^pe  of  the  class  of  factors  now  spoken 
of  as  lethals  (see  p.  196).  Such  mutations,  which 
are  commonly  spoken  of  as  dominants  in  the  hetero- 
zygous condition,  are  really  defects  which  affect  the 
offspring  when  present  on  only  one  side  of  the  house. 


CHAPTER  V 

THE  LIMITS  OF  HEREDITY 

Another  subject  of  great  interest  in  connection  with 
human  inheritance  is  the  question  of  its  hniits. 
Are  there  any  details  of  structure  so  small,  or  of  such 
a  nature,  as  to  be  beyond  the  reach  of  heredity  ? 
Galton  considered  this  subject,  and  in  his  book  on 
Finger  Prints  (1892)  found  such  structures  in  the 
more  minute  details  or  minutiae  of  the  individual 
ridges  of  the  finger-print  patterns.*  We  have  already 
considered  another  case  (p.  74)  in  right  and  left- 
handedness  of  cereals.  Obviouslv  the  observation 
of  human  duplicate  twins  should  throw  much  light 
on  this  subject,  and  since  Galton 's  studies,  in  which 
he  classified  finger-tip  patterns  as  loops,  whorls,  and 
arches,  a  considerable  literature  has  grown  up  which 

*  I  cannot  refrain  from  pointing  out  again  how  closely  Galton 's 
views  agreed  with  some  of  the  current  conceptions  of  continuous 
and  discontinuous  variation.  He  says  [I.e.,  p.  211):  "Not  only 
is  it  impossible  to  substantiate  a  claim  for  natural  selection,  that 
it  is  the  sole  agent  in  forming  genera,  but  it  seems,  from  the 
experience  of  artificial  selection,  that  it  is  scarcely  competent  to 
do  so  by  favouring  mere  varieties,  in  the  sense  in  which  I  under- 
stand the  term. 

"My  contention  is  that  it  acts  by  favouring  small  sports. 
Mere  varieties  from  a  common  typical  centre  blend  freely  in  the 
offspring,  and  the  offspring  of  every  race  whose  statistical  charac- 
ters are  constant,  necessarily  tend,  as  1  have  often  shown,  to 
regress  towards  their  common  typical  centres.  Sports,  on  the 
other  hand,  do  not  blend  freely;  they  are  fresh  typical  centres 
or  sub-species,  which  suddenly  arise,  we  do  not  yet  know  precisely 
through  what  uncommon  concurrence  of  circumstances,  and  which 
observations  show  to  be  strongly  transmissible  by  inheritance." 

175 


176  HEREDITY  AND  EUGENICS 

can  onh^  be  touched  upon  here.  A  full  bibliography 
is  given  b}-  Wilder  (191 6).  The  results  have  shown 
that  not  onh^  the  ridge  patterns  of  the  linger  tips, 
but  also  those  of  the  palms  of  the  hands  and  the  soles 
of  the  feet,  tend  to  be  inherited.  Wilder  gives  some 
striking  instances  of  pecuhar  and  unusual  palm  and 
sole  patterns  appearing  in  parents  and  offspring. 
Thus,  a  man  with  a  calcar  loop  on  both  feet  married 
a  woman  with  a  calcar  loop  and  a  divergence.  Of 
their  three  children,  one  has  a  loop  on  both  feet,  two 
have  a  loop  on  one  foot  and  a  divergence  on  the  other, 
the  loop  being  on  the  right  foot  in  one  case  and  the 
left  in  the  other.  Yet  the  calcar  loop  is  so  rare  as  to 
have  been  found  only  four  times  (aside  from  this 
famil}")  in  1,000  or  more  individuals  examined. 

Twins. 

In  the  case  of  duplicate  or  identical  twins  (Wilder, 
1904)  these  patterns  show  great  similarit}'",  though 
not  identity,  and  there  is  a  distinct  tendenc}^  for 
mirror-image  patterns  to  appear,  especially  on  the 
forefingers.  Light  has  been  thrown  on  the  subject 
of  inheritance  in  twins  by  the  studies  of  Newman 
and  Patterson  (191 1,  191 6)  on  development  and 
variation  in  the  armadillo.  This  animal  always 
produces  four  \^oung  at  a  birth  (some  species  more), 
and  these  are  invariably  of  the  same  sex,  and  have 
been  shown  by  Patterson  (191 3)  to  arise  by  a  process 
of  embryonic  budding  in  the  embryo  derived  from 
a  single  egg. 

Stockard  (1921)  has  recently  suggested  an  ex- 
planation of  this  condition  of  polyembryony  in  the 
armadillo.  The  Texan  species  invariably  produces 
four  young  at  a  birth,  a  South  American  species 
regularl}^  produces  eight,  while  in  certain  species  as 
many  as  twelve  3^oung  may  be  produced,  apparent ty 


THE  LIMITS  OF  IIEREDTTY  177 

from  tertiary  Imclding.  Some  other  species  of 
armadillo  produce  only  one  embr^-o  from  the  e^g. 
In  the  Texas  species  {Tatusia  novcnicincta)  Patterson 
has  shown  that  two  buds  grow  out,  each  of  which 
immediately  divides  into  two.  In  the  species  in 
which  eight  young  are  produced,  these  four  buds 
presumably  divide  again,  while  tertiary  budding  of 
the  embryo  produces  a  higher  number. 

Patterson  (191 3)  found  a  "  period  of  quiescence  " 
in  the  development  of  the  young  blastocyst,  which 
Newsman  believes  to  be  connected  with  the  cause  of 
the  budding.  In  the  gastrula  stage  the  embryo 
remains  quiescent  for  several  weeks.  Then  placenta- 
tion  takes  place,  and  the  development  is  resumed. 
Stockard  (1921)  suggests  that  while  the  blastoc^^st  is 
lying  free  and  unattached  in  the  uterine  cavity,  the 
consequent  absence  of  an  oxygen  supply  {via  the 
blood)  inhibits  development.  This  condition  of  an 
unattached  blastocyst  is  found  in  no  other  mammal 
except  the  deer.  It  is  not  known  wh}'-  the  delay  in 
implantation  of  the  blastoc3'^st  occurs,  but  from 
studies  of  other  mammals  it  is  suggested  that  it  may 
be  due  to  some  peculiarit}^  in  the  formation  of  the 
corpora  lutea.*  In  other  animals,  for  example 
birds,  the  deer,  and  lower  animals,  arrest  of  develop- 
ment does  not  lead  to  pol^^embryony.  But  Stockard 
finds  from  experiments  with  certain  fish  eggs  that, 
if  development  is  arrested  early  (before  gastrulation), 
twins  and  double  embryos  are  frequently  produced. 
Hence  the  interruption  must  occur  at  a  critical  time. 
Also  there  must  be  present  in  the  Qgg,  as  in  that  of 
the  armadillo,  a  decided  tendcmcy  to  form  buds  under 
conditions  of  arrest.  .Ihus  it  appears  that  the 
interaction  of  certain  external  and  internal  forces  is 

*  A  yellow  mass  of  cells  in  the  ovary  in  place  of  a  discharpjcd 

ovum.     If  the  ovum  is  fertilised  the  corpus  luteum  persists  and 

grows  for  several  months.     The  number  of  corpora  lutea  therefore 

corresponds  with  the  number  of  developing  embryos. 

1  2 


178  HEREDITY  AND  EUGENICS 

necessar}?-  to  produce  polyenibryony.*  In  the  deer 
it  is  not  known  when  the  arrest  occurs,  but  failure  of 
budding  (twins)  may  be  due  to  (i)  arrest  being  at 
the  wrong  stage  of  development,  or  (2)  lack  of  a 
tendency"  for  the  embr3^o  to  bud.  Possibly  delayed 
implantation  of  the  blastocyst,  which  may  in  turn 
be  controlled  by  the  condition  of  the  corpora  lutea, 
may  account  for  the  production  of  identical  twins  in 
man.  A  peculiarity^  in  the  activity  of  the  corpora 
lutea  would  be  as  likely  to  be  inherited  as  are 
differences  in  other  glands  of  internal  secretion,  and 
such  a  difference  would  then  become  a  factor  in  the 
inheritance  of  twinning. 

Newman,  who  has  investigated  twinning  for  a 
number  of  3^ears,  published  a  little  book  on  the 
subject  (191 7),  and  has  recently  (1921)  taken  up 
experiments  on  the  production  of  twin  embryos. 
He  used  a  Californian  starfish,  and  studied  the 
twinning  which  may  occur  in  spontaneous^  partheno- 
genetic  larvae  and  in  hybrids  with  another  species. 
He  looks  upon  twinning  as  a  process  which  involves 
the  duplication  of  originally  single  structures.  The 
first  step  involved  is  retarded  development,  followed 
by  loss  of  organisation  or  dedifferentiation.  Re- 
cover}^ results  in  the  formation  of  new  apical  points, 
which  form  the  anterior  ends  of  new  individuals.  In 
the  starfish  Patiria  such  arrested  development  may 
result    in    physiological   isolation    of   blastomeres    in 

*  Regarding  the  interpretation  of  polyembryony  in  the 
armadillo,  Professor  MacBride  suggests  that  all  the  South  Ameri- 
can Edentates  are  originally  descended  from  tree-living  animals, 
in  which  it  is  an  advantage  to  have  only  one  young  at  a  birth, 
and  a  dome-shaped  placenta  as  in  the  apes.  The  armadillos 
have  taken  to  the  ground  where  the  risks  are  greater,  but  have  not 
been  able  to  recover  the  habit  of  laying  more  than  one  egg.  They 
have,  however,  substituted  the  method  of  multiplication  by 
budding  from  the  single  egg.  The  fact  that  in  man  also  identical 
twins  occur  may  similarly  be  a  result  of  his  arboreal  ancestry. 


THE  LnriTS  OF  TTEREDTTY  179 

the  two-  or  four-cell  stage,  or  the  formation  of  double, 
triple,  or  multiple  monsters  in  the  blastula,  gastrula, 
or  larval  (bipinnaria)  stage. 

It  is  of  interest  to  note  in  this  connection  that 
pol^^embryon}^,  through  division  of  the  proembr^-o 
into  four  cells  which  undergo  separate  development, 
is  a  common  feature  in  the  pines  and  in  some  other 
Abietineae,  although  in  Pinus  laricio  it  has  been 
observed  that  a  single  embryo  sometimes  develops 
from  these  four  cells  owing  to  their  failure  to  separate. 
In  an}^  case  only  one  embryo  reaches  maturity,  the 
others  aborting  at  various  stages  of  their  develop- 
ment. It  is  unknown  what  determines  the  cohesion 
or  separation  of  the  four  proembryonic  cells. 

Reversed  symmetry  and  mirror-imaging  are  the 
result  of  a  unit}'  in  development,  and  the  degree  in 
which  these  phenomena  appear  in  twins  furnishes 
evidence  as  to  the  length  of  time  which  the  embryos 
remain  in  contact  during  development.  It  is  now 
generally  agreed  that  double  monsters  are  simply 
conjoined  twins  which  have  failed  to  complete  their 
separation.  Wilder  (191 6)  describes  a  remarkable 
case  of  double  twins  (girls)  of  the  extremely  rare 
pygopagous*  type.  Their  four  palms  are  practically 
alike  in  ridge  pattern.  Three  of  the  soles  are  also 
alike,  but  the  fourth  is  radically  different.  Curiously 
enough,  the  data  concerning  the  palm  and  sole 
patterns  of  the  parents,  which  are  necessary  for  an 
evaluation  of  the  inheritance,  are  not  mentioned,  and 
this  limits  the  interpretation  of  the  facts.  One  cannot, 
therefore,  say  that  the  aberrant  pattern  is  beyond 
hereditary  control. 

The  famous  Blazek  twins,  who  were  born  in 
Bohemia  and  recently  died  in  Chicago  at  the  age  of 
forty- four,  are  apparently  another  case  of  pygopagy. 
One  of  them  was  married  and  gave  birth  to  a  son, 

*  Joined  by  the  buttocks. 


i8o  HEREDITY  AND  EUGENICS 

now  eleven  years  of  age.  Whether  they  were  of  the 
identical  type  is  not  stated,  but  they  were  said  to 
differ  in  disposition  and  tastes,  although  they  are 
stated  to  have  had  only  one  set  of  digestive  and  pro- 
creative  organs.  The\^  both  nursed  the  infant  son, 
and  food  eaten  b}^  one  benefited  the  other.  As  they 
left  no  wills,  litigation  is  now  pending  to  determine 
whether  the}^  should  be  legally  considered  one  or  two. 

A  similar  case  of  united  twins  is  described  by 
Sullivan  (191 9).  These  twin  bo3^s  were  ten  ^^ears  old 
when  examined,  and  w^ere  born  in  Samar  Island, 
Philippines.  They  are  identical  twins  in  which  the 
separation  has  been  incomplete,  the  right  buttock  of 
one  being  in  juncture  with  the  left  buttock  of  the 
other,  and  the  terminal  part  of  the  alimentary  canal 
is  a  single  structure.  The}^  are  otherwise  normal 
and  intelligent,  having  yellowish-brown  skin  colour, 
straight  black  hair  and  dark  brown  eyes.  But  the 
left  twin  is  right-handed  and  the  right  twin  left- 
handed.  The  latter  also  has  more  rounded  ears  closer 
to  his  head,  is  somewhat  taller,  and  probably  more 
often  takes  the  initiative.  There  are  marked 
differences  in  the  proportions  of  the  head  and  face, 
both  being  somewhat  asymmetrical  and  laterally 
distorted  to  the  right  in  the  right  twin  and  to  the  left 
in  the  left  twin.  Hence  the  distortion  is  probably  due 
to  external  influences  and  developmental  disturbances. 
The  finger  prints  are  very  similar,  but  with  minor 
differences  in  configuration. 

Danforth  (191 9)  has  dissected  the  left  hands  of  a 
pair  of  poly  dactyl  negro  infant  tw^ins,  and  compared 
them  with  a  normal  white  infant.  It  is  uncertain 
whether  they  were  identical  (uniovular)  twins.  The 
polydactylism  consisted  in  a  small,  nearly  globose, 
mass  on  each  hand  w^ith  a  slender  attachment  to  the 
little  finger.  This  extra  digit  bore  a  nail  and  friction 
ridges.     It  is  thought  that  Polydactyly  of  this  type 


THE  LIMITS  OF  HEREDITY  i8i 

may  have  its  greatest  expression  early  in  ontogeny, 
before  birth,  and  that  it  may  be  induced  either  by 
hereditary  or  other  factors.  The  twins  showed 
marked  similarit}^  in  their  friction  ridge  patterns, 
also  in  the  muscular  and  arterial  systems  of  their 
hands,  some  similarity  in  nerve  distribution,  but 
practically  no  resemblance  as  regards  the  veins. 
Compared  with  the  control  hand,  these  resemblances 
indicate  that  heredity  is  the  chief  factor  involved  in 
the  variations  observed. 

Newman  and  Patterson  (191 1)  have  made  a  study 
of  the  inheritance  of  peculiarities  in  the  scutes  or  scales 
on  the  nine  bands  of  the  armadillo,  and  similar 
phenomena  to  those  above  mentioned  (p.  179)  appear 
in  their  quadruplets,  but  in  all  these  cases  the  father 
is  unknown.  Thus,  in  one  set  of  quadruplets  three 
show  a  double  or  abnormal  scute,  and  one  lacks  it ; 
in  another  set  three  have  the  scapular  double  scute, 
and  one  lacks  it.  Other  sets  of  quadruplets  show 
more  variation  in  the  position  of. abnormal  scutes, 
but  the  evidence  indicates  that  the  latter  are,  at  any 
rate,  blastogenic  or  predetermined  in  the  egg.  The 
authors  attribute  these  divergencies  to  inaccuracy 
in  the  bilateral  distribution  of  hereditary  materials 
during  development — in  other  words,  to  somatic 
segregation.  The  element  of  heredity  cannot  be 
accurately  judged  without  a  knowledge  of  the  male 
parents.  The  process  of  scute  alignment  is  shown  to 
be  largely  mechanically  determined,  and  hence  beyond 
the  limits  of  hereditary  control. 

Newman  (191 6)  finds  in  armadillo  quadruplets  a 
condition  of  symmetry  between  that  observed  in 
double  monsters  (whose  whole  development  has  been 
in  contact),  and  human  duplicate  twins.  Hence  he 
concludes  that  the  latter  become  ''physiologically 
isolated  "  (this  may  imply  asymmetrical  nuclear 
divisions  of  cells  whose  descendants  remain  tor  some 


I  82 


HEREDITY  AND  EUGENICS 


time  in  contact)  considerably  earlier  in  development 
than  do  armadillo  quadruplets.  Indeed,  the  amount 
of  mirror-imaging  is  so  small  in  human  duplicate  twins 
that  it  appears  probable  that  the  separation  (actually 
of  cells  or  ph3^siologically  of  nuclear  elements)  takes 
place  early  in  the  cleavage,  though  not  necessarily 


Fig.   30. — ^TwiN  American  Sailors  of  Irish  Birth. 

at  the  first  cleavage  of  the  egg,  as  was  formerly 
supposed.  It  should  be  pointed  out  that  this  line  of 
reasoning,  while  attractive,  is  not  necessarily  con- 
clusive according  to  the  present  state  of  our  know- 
ledge. 

A  typical  case  of  finger-print  patterns  in  duplicate 


THE  LIMITS  (3F  HEREDITY 


183 


twins  is  given  in  the  Journal  of  Heredity,  November, 
1 91 6  (see  Figs.  30,  31).  The  patterns  are  ahke  in 
these  two  men,  except  that  the  thumb  of  the  left  hand 
has  a  loop  in  one  twin  and  a  whorl  in  the  other,  while 
the  middle  finger  in  the  former  has  an  arch,  and  in  the 
latter  a  loop.  Moreover,  in  each  twin  the  patterns 
on  the  fingers  of  the  left  hand  are  in  nearly  every  case 
mirror-images  of  the  patterns  on  the  corresponding 


UEF-T      ►-<  AN  O. 


UEF-X     MAMO. 


7      ,"■{ 


£r  ^^     '=iM>  ■'* 


^x^- 


RIO  WT     M  A^J  O. 


% 


'■\ 


RIOMT      H  AM  O. 


m 


Fig.  31. — Finger  Prints  of  the  Twins  in  Fig.  30. 

The  thumbs  of  their  left  hands  and  the  middle  fingers  of  their 
right  hands  are  clearly  distinguishable  in  pattern. 

fingers  of  the  right  hand.  Another  evidence  that 
these  friction-skin  patterns  are  on  the  borders  of 
hereditary  control  is  found  in  the  fact  that  in  a 
congenitally  split  finger  observed  b}'  Wilder  the 
patterns  of  the  two  finger  tips  were  not  identical.  In 
all  hands  the  minutiae  of  the  ridges,  such  as  forkings, 
interruptions,  and  isolations,  remain  constant  through- 
out life,  and  these  form  the  basis  for  the  identification 


1 84 


HEREDITY  AND  EUGENICS 


systems.  These  details  are  clearly  not  inherited, 
for  no  two  patterns  are  alike  in  these  particulars, 
and  Galton  concluded  that  the  chance  of  two  finger 
prints  being  identical  was  less  than  i  in  64,000,000,000. 
The  inheritance  of  finger-print  patterns  is  the 
subject  of  a  paper  by  Miss  Elderton  (1920).  The 
arch,  loop,  whorl,  and  composite  are  the  types  of 
pattern  used  for  criminal  classification.  But  this  is 
inadequate  for  scientific  distinctions.  Galton  in- 
creased his  four  or  five  original  categories  up  to  fifty- 
three.     He  was   led   to    assume    continuity    between 


Fig.  32. — Twins,  Eighteen  Years  of  Age,  from  York, 

Pennsylvania. 


types,  and  for  years  sought  quantitative  measures 
for  the  finger  print.  Miss  Elderton  adopts  the  follow- 
ing order,  arch,  small  loop,  large  loop,  composite, 
whorl,  as  a  natural  order  in  passing  from  type  to  type. 
An  effort  was  made  to  state  the  inheritance  in 
Mendelian  terms.  The  difficulties  were  (i)  in  the 
presence  of  transitional  forms;  (2)  there  is  probable 
inheritance  of  pattern  with  change  of  finger.  As- 
suming that  inheritance  was  on  the  same  finger  from 
parent  to  offspring,  and  classifying  Galton 's  data,  she 
found  that :  (i)  Arch  x  arch  and  arch  x  composite  ap- 
pear to  give  no  whorls ;  (2)  whorl  x  whorl  and  whorl 


THE  LIMITS  OF  HEREDITY 


i8 


X  composite  give  no  arches;  (3)  arch  x  loop,  whorl 
X  loop,  composite  x  loop,  and  loop  X  loop  can  give 
all  four  types ;  (4)  composite  is  rare,  but  it  may  be 
that  composite  x  composite  cannot  give  arches ; 
(5)  arch  X  whorl  can  give  all  types.  These  results 
suggest  that  loop  is  '*  much  more  heterozygous  "  than 
arch  or  whorl.  If  composite  is  combined  with  loop, 
simpler    ratios    are    obtained.     But    the    Mendelian 


Fig.  33, — ^TwiNs  having  the  same  Height,  Weight,  Tastes, 

Disposition,  and  Talents. 

They  have  worked  together  for  twenty-five  years  and  have  never 

been  separated. 

interpretation  is  unsatisfactory  (i)  because  it  is 
unjustifiable  to  combine  composite  with  loops;  (2)  be- 
cause the  categories  are  really  not  sharp,  but  a  great 
variety  of  transitional  forms  occurs;  and  (3)  there  is 
good  reason  to  believe  that  inheritance  is  not  neces- 
sarily from  one  finger  of  the  parent  to  the  same  finger 
of  the  child.  The  coefficient  of  inheritance  method 
of  treatment  gives  low  values  of  inheritance. 


I  86 


HEREDITY  AND  EUGENICS 


The  brain  convolutions  in  duplicate  twins  have 
also  been  compared.  For  example,  Sano  (191 6) 
studied  the  brains  of  stillborn  twin  boys.     One  boy 


Fig.  34. — ^TwiNs  from  Battle  Creek,  Michigan. 

They  were  separated  when  three  years  of  age,  and  have  always 
lived  apart.  Even  their  best  friends  cannot  distinguish 
them  when  they  meet. 

was  somewhat  larger  throughout  than  the  other, 
and  this  applied  also  to  the  brains,  the  larger  brain 
being  more  highly  developed,  with  more  sulci.     But 


Fig.  35. — Twin  Sisters  from  Romanshorn,  Switzerland. 

there  was  a  very  remarkable  similarity  in  the  dis- 
position of  the  furrows,  and  all  the  differences  were 
of  secondary  importance,  thus  indicating  the  in- 
heritance of  similar  mentalities. 


THE  LIMITS  OF  HEREDITY  187 

Galtoii  (1883)  made  a  study  of  twins,  which  con- 
tains many  facts  of  great  interest.  In  response  to 
inquiries  he  obtained  descriptions  of  about  eighty 
pairs  of  closely  similar  twins,  thirty-live  of  which 
entered  into  full  details.  He  says  (p.  21C):  "  In  a 
few  of  these  not  a  single  point  of  difference  could  be 
specified.  In  the  remainder  the  colour  of  the  hair 
and  eyes  was  almost  always  identical;  the  height, 
weight,  and  strength  were  nearly  so.  Nevertheless, 
I  have  a  few  cases  of  a  notable  difference  in  height, 
weight,  and  strength,  although  the  resemblance  was 
otherwise  very  near.  The  manner  and  personal 
address  of  thirty-five  pairs  of  twins  are  usually 
described  as  very  similar,  but  accompanied  by  a 
slight  difference  of  expression,  familiar  to  near 
relatives,  though  unperceived  by  strangers.  The 
intonation  of  the  voice  when  speaking  is  commonl}' 
the  same,  but  it  frequently  happens  that  the  twins 
sing  in  different  keys.  Most  singularly,  the  one 
point  in  which  similarity  is  rare  is  the  handwriting. 
I  cannot  account  for  this,  considering  how  strongl}' 
handwriting  runs  in  families,  but  I  am  sure  of  the 
fact.  I  have  only  one  case  in  which  nobody,  not 
even  the  twins  themselves,  could  distinguish  their 
own  notes  of  lectures,  etc.,  barely  two  or  three  in 
which  the  handwriting  w^as  undistinguishable  by 
others,  and  only  a  few  in  which  it  was  described  as 
closely  alike.  On  the  other  hand,  I  have  many  in 
which  it  is  stated  to  be  unlike,  and  some  in  which 
it  is  alluded  to  as  the  only  point  of  difference.  It 
would  appear  that  the  handwriting  is  a  ver}-  delicate 
test  of  difference  of  organisation— a  conclusion  which 
I  commend  to  the  notice  of  enthusiasts  in  the  art  ol 
discovering  character  by  handwTiting."* 

Galton  cites  a  number  of  remarkable  similarities 
in   these   thirt3'-five   pairs   of  twins   and   others.     In 

*  Cf.  p.  172. 


1 88  HEREDITY  AND  EUGENICS 

seven  of  the  thirty- five,  both  twins  "  suffered  from 
some  special  ailment  or  had  some  exceptional 
peculiarity.  Two  twins  at  the  age  of  twenty-three 
were  attacked  by  toothache,  and  the  same  teeth  had 
to  be  extracted  in  each  case."  A  pair  of  French  twins 
who  travelled  as  business  men  and  were  asthmatic 
always  had  attacks  in  the  same  cities.  They  were 
taken  simultaneously  with  rheumatic  ophthalmia 
(an  inflammation  of  the  eye),  one  in  Paris,  and  the 
other  in  Vienna.  In  another  French  case  the  twins 
were  monomaniacs,  melancholy,  morose,  suffering 
from  imaginary  persecutions,  etc.  They  showed 
precisely  the  same  symptoms,  although  always  kept 
apart  and  never  communicating  with  each  other. 
At  intervals  of  months  the  same  mental  changes 
would  spontaneously  come  over  them  both  inde- 
pendently, even  when  they  w^ere  in  institutions  some 
miles  apart. 

In  eleven  of  the  thirty-five  pairs  of  twins  cited  by 
Galton  there  was  the  same  association  of  ideas,  twins 
often  making  the  same  remarks  on  the  same  occasion, 
or  beginning  to  sing  the  same  song  at  the  same  time. 
One  twin  visiting  Scotland  bought  a  set  of  champagne 
glasses  as  a  surprise  for  his  brother  B.  The  brother 
in  England  at  the  same  time  bought  a  set  of  precisely 
the  same  pattern  for  his  brother  A.  In  sixteen  cases 
the  twins  were  closely  similar  in  tastes  and  dis- 
positions. The  differences  in  the  others  were  merely 
in  intensity  or  energy,  one  being  more  vigorous,  the 
other  more  gentle,  etc.  The  mental  similarities 
evidently  extended  to  the  fundamental  structure  of 
the  mind,  and  were  not  merely  superficial.  In  only 
two  cases  was  a  strong  bodily  resemblance  accom- 
panied by  mental  diversity,  and  the  converse  occurred 
only  once.  Clearly  a  more  extended  study  of  the 
mental  differences  between  identical  twins  will  throw 
valuable   light    on    questions    of   mental   inheritance. 


THE  LIMITS  OF  HEREDITY  i  <S9 

The  records  of  similar  twins  show  that  ilhicsses 
clearly  retard  i^rowth,  and  may  thus  cause  permanent 
differences  between  twins.  Some  inherited  differences 
also  first  develop  late  in  life. 

The  number  of  the  Journal  of  Heredity  for  December, 
1 91 9,  is  devoted  entirely  to  twins,  and  contains 
thirty  figures,  chiefly  photographs  of  twins,  which 
show  remarkable  degrees  of  resemblance.  One  ]jair 
of  grown-up  brothers  have  not  only  identical  features, 
but  the  same  height  and  weight,  the  same  tastes, 
disposition,  and  talent.  Another  pair  of  identical 
twins  of  exceptional  abilit}"  have  never  differed 
more  than  a  pound  in  weight,  never  varied  more 
than  o-i  per  cent,  in  their  college  marks,  and  although 
absolutely  dependent  upon  glasses,  can  wear  each 
other's.  Their  illnesses  have  often  coincided,  and 
most  of  their  tastes  are  similar.  But  their  tailor  says 
that  one  of  the  twins  has  a  short  left  arm  and  the 
other  a  short  right  arm — a  mirror-image  difference 
such  as  frequently  occurs  in  twins.  Several  pairs  of 
these  twins  are  illustrated  in  Figs.  30  to  35. 

The  record  of  identity  in  another  case  extends  to 
size,  voice,  and  tastes  in  music,  but  they  differ  in 
their  taste  for  mathematics.  Twins  which  were 
separated  at  three  years  of  age  (Fig.  34),  and  have 
since  remained  apart,  show^  an  equall}'  striking 
identity  of  features.  The  handwriting,  which  is 
known  to  be  an  index  of  character,  is  closely  alike 
in  many  twins,  in  one  case  "  virtually  identical," 
but  differences  are  also  recorded. 

There  are  clearly  differences  in  the  degree  of 
resemblance  between  *'  identical  "  twins.  One  pair 
of  men  twins  agree  in  features  and  in  their  likes  and 
dislikes,  diversions,  foods,  and  intellectual  interests. 
They  both  suffer  from  night-blindness,  but  their  hand- 
writing is  "  very  different."  Another  pair  have 
similar  tastes  for  poetry  and  music,  and  enjoy  the 


I  go  HEREDITY  AND  EUGENICS 

same  sports,  but  differ  in  their  mathematical  tastes 
and  in  their  gait.  One  was  left-handed  as  a  child, 
but  their  writing  is  strikingly  alike,  and  they  both 
have  the  same  peculiarity  of  the  left  thumb  joint. 
They  differ  in  application  and  in  nervousness.  This 
is  a  striking  combination  of  similarities  with  minor 
differences  and  an  unaccountable  left-handedness 
in  one. 

Still  another  pair  of  men  of  fift3^-nine  show  less 
identity  of  feature,  but  similar  gait  and  bodily 
weaknesses,  the  same  dislike  for  strawberries  and  acid 
foods,  and  a  congeniality  for  each  other  which  appears 
to  be  characteristic  of  identical  twins .  But  their  ocular 
defects  pertain  to  the  right  eye  in  one  and  the  left  eye 
in  the  other,  and  their  handwTiting  is  not  strikingly 
similar,  though  showing  marked  resemblances. 

Popenoe  (1922)  has  recently  described  a  case  in 
which  twin  girls  were  reared  separately  and  have  led 
very  different  lives  yet  maintain  their  physical  and 
mental  identity.  The  mother  died,  and  they  were 
separated  at  the  age  of  eight  months.  They  did  not 
see  each  other  again  or  correspond  until  they  were 
eighteen,  and  have  only  been  together  for  about  ten 
months  in  all  their  lives.  One  married  and  taught 
in  a  school,  the  other  travelled  and  has  followed 
a  business  career  in  various  parts  of  the  country. 
Yet  they  remain  of  exactly  the  same  height  and  can 
wear  each  other's  clothes.  Their  hair  and  voices  are 
the  same  and  people  cannot  tell  them  apart.  They 
even  both  had  their  hair  bobbed  at  the  same  time, 
each  without  the  other  knowing  it.  Their  intellectual 
capacities  appear  to  be  very  similar,  as  well  as  their 
tastes.  Like  many  twins,  their  illnesses  also  usually 
came  at  the  same  time.  Here  is  an  excellent  example 
showing  the  overpowering  importance  of  nature, 
and  the  insignificance  of  environment  and  experience 
m  producing  differences. 


THE  LIMITS  OF  HEREDITY  191 

One  of  the  interesting  facts  concerning  "  identical  " 
twins  which  emerges,  and  has  already  been  shown  in 
other  data,  is  (i)  that  they  differ  in  their  degree  of 
resemblance;  (2)  that  they  ma}^  show  exceptional 
similarity  in  most  respects,  and  marked  divergence 
in  a  few.  The  former  fact  can  probably  be  accounted 
for,  as  explained  above,  on  the  basis  of  an  earlier  or 
later  separation  of  blastomeres,  or  of  the  budding 
rudiments  of  separate  embryos.  Marked  divergence 
in  certain  characters  was  also  obtained  in  armadillo 
quadruplets,  together  with  mirror- image  effects. 
The  explanation  is  doubtless  the  same  in  both  cases, 
but  is  not  clear  at  the  present  time,  unless  it  be  that 
the}^  are  biovular  twins  from  parents  heterozygous 
only  in  these  characters.  A  certain  amount  of 
divergence  must  be  expected  even  between  identical 
twins,  just  as  the  two  sides  of  the  face,  or  the  measure- 
ments of  any  bilaterally  symmetrical  organs  of  the 
body  ma}^  show  differences.  It  is  a  more  puzzling 
fact  that  this  bilateral  asymmetry  is  itself  inherited, 
as  shown  b}^  identical  twins  whose  faces  show  exactl}' 
the  same  asymmetries  (Fig.  34). 

A  fact  in  this  connection  which  is  frequently  for- 
gotten is  that  the  only  reason  why  human  identical 
or  monozvsfotic  twins  more  closelv  resemble  each 
other  than  ordinary  brothers  and  sisters  is  because 
man  is  usually  heterozygous  for  so  many  characters 
that  the  chances  of  two  different  germ-cells  from  the 
same  parents  furnishing  exactly  the  same  combination 
of  characters  is  remote.  Nevertheless,  it  is  un- 
doubtedly the  fact  that  in  some  families  in  which  both 
parents  are  homozN'gous  for  many  characters,  brothers 
or  sisters  ma}',  and  do,  occasionally  occur  from 
separate  births,  and  yet  resemble  each  other  as  much 
as  identical  twins,  except  that  there  is  always  an  age 
difference.  Biovular  twin  births  in  such  families 
may  be  expected  to  give  rise  occasionally  to  twins 


192  HEREDITY  AND  EUGENICS 

which  appear  to  be  of  the  "  identical  "  type,  except 
in  one  or  two,  or  a  few  characters  in  which  the 
parents  were  heteroz3^gous  and  the  germ  cells  con- 
cerned happened  to  carry  the  corresponding  allelo- 
morphic  characters. 

We  are  so  accustomed  to  seeing  diversity  in  the 
offspring  from  a  single  pair  of  human  parents  that 
we  forget  what  always  happens  in  crosses  of  homo- 
zygous types.  Any  plant  breeder  will  have  made 
numerous  crosses  in  which  the  F^  offspring  are  so 
absolutely  alike  as  to  be  indistinguishable  by  any 
visible  differences,  or  probabh^  even  any  constant 
measurable  difference.  There  is  no  doubt  that,  for 
similar  reasons,  what  appear  to  be  identical  or 
monozygotic  twins  occasionally  appear  in  human 
families  when  they  are  really  dizygotic  or  ordinary 
twins  of  the  same  sex.  This  clearly  helps  to  account 
for  the  occurrence  of  intermediates  between  identical 
and  fraternal  twins — i.e.,  twins  of  the  same  sex  which 
differ  only  in  a  very  few  characters. 

Windle  (1892)  has  collected  numerous  cases  of 
identical  malformations  in  twdns,  many  of  which 
were  known  to  be  of  the  identical  type,  although, 
unfortunately,  the  sex  is  specifically  mentioned  in  only 
one  or  two.  A  case  is  described  of  twins  enclosed  in 
the  same  membranes,  in  both  of  which  there  was  a 
deficiency  of  the  anterior  abdominal  wall,  the  in- 
testines and  part  of  the  liver  being  contained  in  a  thin 
membranous  sac.  Another  sac,  the  size  of  a  walnut, 
hung  posteriorly  from  between  the  thighs.  The 
latter  was  probably  due  to  persistence  of  the  neuren- 
teric  canal,  dilated  by  the  rachidian  fluid  to  form  a 
sac.  Instances  in  which  both  twins  have  the  same 
malformation  are  said  to  be  not  uncommon.  But  in 
Rotunda  Hospital,  Dublin,  in  the  years  1 847-1 854, 
there  were  13,748  women  delivered,  of  whom  233 
had  twins  (  =  1  in  59),  none,  however,  showing  similar 


THE  LIMITS  OF  HEREDITY  193 

malformations.  Windle  cites  numerous  instances 
from  the  literature,  including  two  cases  of  twins,  both 
showing  hypospadias;  (3)  one  pair  with  hermaphro- 
ditismus  masculinus ;  (4)  one  with  occipital  meningo- 
celes* of  the  same  size,  and  hypospadias  as  well; 
(5)  one  of  spina  bifida  ;t  (6)  occipital  meningocele  with 
the  upper  and  low  extremities  one-quarter  their  normal 
length  (considered  phocomeliaj) ;  (7)  anencephali 
(without  a  brain),  the  palates  1  also  having  a  deep 
longitudinal  furrow;  (8)  male  twnns,  both  with  right- 
sided  congenital  hydrocele  ;§  (9)  twins  with  cyclopia 
(one  median  eye);  (10)  twin  girls  with  abnormally 
developed  sex  organs,  christened  as  boys;  (11)  twins 
with  six  digits  on  hands  and  feet  (in  one  amnion) ; 
(12)  twins  with  a  supernumerary  pollex  (thumb)  on 
the  right  hand;  (13)  one  twdn  with  six  fingers,  the 
other  with  six  fingers  and  six  toes;  (14)  twans  with 
a  sternalis  muscle,  the  mother  also  having  one; 
(15)  twins  with  a  remarkable  conformation  of  the  left 
parietal  bone;  (16)  cited  b}^  Galton,  a  pair  of  twins 
with  slight  congenital  flexure  of  one  of  the  joints  of 
the  little  finger.  The  condition  was  inherited  from 
a  grandmother,  but  neither  parents  nor  sisters  nor 
brothers  show  any  trace  of  it.  (17)  Twins  with  a 
peculiar  way  of  bending  their  fingers.  There  is  a 
faint  tendency  to  the  same  peculiarity  in  the  mother, 
but  in  no  other  member  of  the  family.  (18)  Cited 
b}^  Darwin,  twins  with  a  crooked  little  finger,  but 
no  know^n  family  tendency  to  this  peculiarity. 

*  Hernial    protrusion    in    the    occipital    region    of    the    three 
membranes  surrounding  the  spinal  cord. 
t  Congenital  cleft  of  the  vertebral  column. 
j  A  condition  with  hands  and  feet,  but  no  arms  or  legs. 
§  A  collection  of  fluid,  occurring  especially  in  the  scrotum. 


13 


194  HEREDITY  AND  EUGENICS 

Inheritance  of  Twinning. 

Interesting  studies  have  recently  been  made  on 
the  inheritance  of  twinning.  It  is  well  known  that 
a  tendency  to  produce  twins  is  inherited  in  sheep, 
certain  breeds  nearly  always  bearing  twins.  Daven- 
port (1920)  places  the  frequenc}^  of  twin  births  at 
about  II  per  cent.,  and  Bonnevie  (1919^)  finds,  from 
statistics  of  human  births  in  Norway,  that  i  -34  per 
cent,  of  births  are  twins.  In  one  Norwegian  family, 
however,  the  frequenc}^  of  twin  births  was  as  high  as 
19-5  per  cent.,  showing  a  strong  tendenc}^  to  in- 
heritance. It  is  significant  that  twinning  occurs  more 
often  in  large  than  in  small  families.  In  the  families 
investigated,  20  per  cent,  of  the  twin  births  were 
believed  to  be  uniovular — i.e.,  derived  from  a  single 
impregnated  Qgg.  It  is  suggested  that  the  tendency 
to  produce  biovular  or  non-identical  twins  is  a 
recessive  character,  but  this  conclusion  does  not 
appear  very  probable. 

In  a  statistical  stud}^  of  twinning  in  families, 
Davenport  (1920)  considers  families  in  which  twin 
births  had  occurred  more  than  once.  The  mothers 
and  fathers  of  such  families  are  spoken  of  as  repeaters. 
If  inheritance  of  twinning  were  onl}^  through  the 
mother,  then  the  relatives  of  repeating  mothers  should 
show  a  higher  proportion  of  twins  than  the  relatives 
of  repeating  fathers.  It  was  found,  however,  that  of 
355  labours  occurring  to  the  mothers  of  repeating 
mothers,  16  or  4-5  per  cent,  were  twin  labours;  while 
of  289  labours  occurring  to  the  mothers  of  twin- 
repeating  fathers,  12  or  4-2  per  cent,  produced  twins. 
Thus,  twins  occur  with  nearly  equal  frequency  in  the 
fraternities  of  repeating  fathers  and  mothers,  and  with 
about  four  times  their  frequency  in  the  general  popu- 
lation. These  and  similar  statistics  indicate  that,  in 
strains  bearing  two  or  more  pairs  of  twins  to  a  family, 


THE  LIMITS  OF  HEREDITY  195 

the  hereditary  influence  of  the  father  on  twin  produc- 
tion is  approximately  equal  to  that  of  the  mother.  In 
thirty  families  containing  twins  classed  as  identical, 
both  the  fathers  and  the  mothers  belonged  to  fra- 
ternities in  which  there  were  13  per  cent,  twin  births. 
Hence  the  inheritance  factor  in  the  production  of 
identical  twins  is  nearly  three  times  as  strong  as  in 
the  production  of  twins  in  general,  and  again  the  in- 
fluence of  the  father  appears  to  be  as  great  as  that 
of  the  mother. 

The  sex  of  twins  is  also  used  as  a  means  of  deter- 
mining how  many  are  probably  biovular  or  uniovular 
in  origin.  In  160  pairs  of  twins  in  repeater  families 
(having  two  or  more  pairs  of  twins),  in  which  the  sex 
was  given,  fifty- four  w^ere  of  unlike  sex  and  106  of 
like  sex.  Since  the  expectation  for  two-egg  twins 
is  an  equalit}'  of  like  and  unlike  sexed  twins,  the 
excess  of  fifty-two  pairs  of  like-sexed  twins  was 
probably  uniovular  in  origin.  This  indicated  that 
about  I  in  3  of  the  twin  births  are  of  identical  twins. 
Davenport  has  also  examined  families  in  which  one 
parent  of  twins  has  married  twice.  In  fourteen  cases 
the  father  married  twice,  in  fifteen  the  mother,  and 
in  one  family  both  father  and  mother.  Where  the 
father  had  married  twice,  there  were  twins  of  both 
marriages  in  tw^o  cases,  or  14  per  cent.,  and  the  corre- 
sponding figure  where  the  mother  had  remarried  was 
21  per  cent.,  again  indicating  by  these  high  values 
the  hereditary-  nature  of  twinning. 

Until  recently  it  would  have  appeared  absurd  that 
the  father  could  have  any  hereditary'  influence  on 
twinning,  but  Davenport  points  out  how  our  present 
knowledge  provides  the  basis  for  such  a  result,  at  least 
as  regards  biovular  or  fraternal  twins.  In  the  first 
place,  there  is  evidence  to  show  that  the  simultaneous 
release  of  two  eggs  is  much  more  frequent  than  are 
twin  births.     There  is  statistical  evidence  from  the 


196  HEREDITY  AND  EUGENICS 

examination  of  corpora  lutea  (see  p.  i  'j'j)  that  5  to  6  per 
cent,  of  ovulations  are  probably  double.  When  the 
number  of  corpora  lutea  of  pregnant  rabbits  and  pigs  is 
compared  with  the  number  of  embryos,  there  is  found 
to  be  always  an  excess  of  the  former,  indicating 
that  some  eggs  fail  to  be  fertilised  after  ovulation. 
Blighted  embr3^os  are  also  repeatedly  found.  They 
account  for  some  of  the  human  cases  of  earh'  mis- 
carriages. Such  cases  are  by  no  means  always  due 
to  physiological  causes,  but  are  often  to  be  explained 
by  inability  of  the  embryo  to  complete  its  develop- 
ment. Lethal  factors  w^hich  kill  the  embr3^o  or 
inhibit  its  development  beyond  a  certain  point  when 
present  in  homozygous  condition  are  now^  well  known 
through  the  work  of  Morgan  and  his  pupils  with  the 
fruit  fly  Drosophila.  It  has  long  been  known  that 
onty  mice  heterozygous  for  yellow  body  colour  can 
live,  and  it  has  recently  been  shown  that  when  such 
3^ellow  mice  are  crossed  with  each  other,  25  per  cent, 
of  the  embryos — i.e.,  the  homoz^^gous  yellows — are 
atretic  and  fail  to  develop. 

Such  evidence  makes  it  certain  that  double  ovula- 
tions are  much  more  frequent  than  twin  births.  This 
will  be  due,  as  Davenport  points  out,  to  (i)  a  failure 
of  fertilisation  of  one  egg,  or  (2)  a  failure  of  develop- 
ment of  one  egg.  Of  course,  lethal  factors  may  be 
present  in  both  ^gg  and  sperm,  and  their  presence 
will  probably  account  for  many  cases  of  sterilit}'  in 
mankind.  Thus  a  woman  may  be  sterile  with  one 
husband  and  fertile  with  another,  or  a  man  may  have 
children  by  one  wife  and  not  by  another.  Couples 
desiring  children  not  infrequenth'  fail  to  produce 
them.  In  some  of  these  cases  the  germ  cells  of  both 
ma}^  contain  the  same  lethal  factor,  or  a  combination 
of  factors  which  are  incompatible  with  development. 
It  is  w^ell  known  that  dairy  cattle  show  similar 
phenomena,    a    particular    bull    being    sterile    with 


THE  LIMITS  OF  HEREDITY  197 

certain  cows.  Gynecological  literature  abounds  with 
cases  of  blighted  twins,  or  of  single  births  accom- 
panied by  an  undeveloped  foetus.  Probably  the 
presence  of  lethal  factors  in  some  of  the  germ  cells 
accounts  for  many  such  cases.  We  have  already 
seen  (p.  90)  that  brach3^dactyh'  is  perhaps  lethal  in 
its  effects  w^hen  present  in  the  homozygous  condition, 
and  the  same  is  probably  true  of  various  other 
abnormalities.  Ihe  conception  of  lethal  factors  is 
thus  destined  to  play  an  important  part  in  the  ex- 
planation of  many  phenomena  of  reproduction  in 
man,  and  to  furnish  an  explanation  of  sterility  in  some 
cases  where  there  has  been  no  voluntary  prevention 
of  children. 

A  remarkable  instance  of  a  strain  producing  multiple 
births  has  recenth^  been  described  (Davenport,  191 9). 
A  woman  living  in  Cleveland,  Ohio,  has  in  three 
successive  marriages  never  had  a  single  child  at  a 
birth.  She  was  born  in  Paris,  and  her  mother  and 
her  mother's  mother  are  both  said  to  have  had  only 
twins,  triplets,  or  quadruplets.  By  her  first  husband 
she  had  twins.  When  he  died  she  married  a  French- 
Canadian,  and  bore  twins,  a  boy  and  a  girl.  The  girl 
married  and  bore  first  a  single  child,  and  then  twins, 
who  died  with  the  mother  shortly  after  birth.  The 
original  mother  next  bore  triplets  ?  ?  c^  who  died  young. 
Two  years  later  twins  ?  S  were  born,  and  again  the 
following  year  twins  ?  S  •  By  a  third  husband  of 
English  and  Scotch  descent  she  had  twins  S  c^ ,  who 
died  young,  then  triplets  c^  ?  ?  ,  a  boy  still  living  and 
two  others  born  dead.  This  was  followed  by  a 
miscarriage  of  triplets  ^  ?  5  ,  then  twins  ?  c^ ,  the  girl 
dying  shortly  after  birth.  Next  followed  a  mis- 
carriage of  quadruplets  (^  c?  ?  ?  ,  caused  by  poor  health 
of  the  mother.  Twins  ^  ?  followed,  the  girl  dying  in 
ten  days,  then  triplets  were  born  c?  ?  ?  ,  the  boy  sur- 
viving.    In  1912   quadruplets,  girls,  were   born;  the 


198  HEREDITY  AND  EUGENICS 

same  year  occurred  a  miscarriage  of  four  boys,  and 
the  following  year  a  miscarriage  of  three  girls.  This 
makes  a  total  of  fort3'-two  births  and  miscarriages 
from  the  one  mother.  In  this  remarkable  case  the 
tendency  to  multiple  births  has  been  traced  in  four 
generations. 

Hayden  (1922)  describes  a  case  of  a  pure-bred 
Holstein-Friesian  cow  in  the  herd  of  the  Ohio 
Agricultural  Experiment  Station  which  has  had  twin 
calves  five  times  out  of  seven  by  three  different  bulls. 
A  more  remarkable  case  is  described  by  Pearl  (191 2), 
who  remarks  that:  ''It  is  well  established  that  a 
tendency  to  multiple  gestation  in  normally  uniparous 
forms  may  be  inherited."  A  Guernsey  cow  pro- 
duced fourteen  calves  in  her  first  eight  pregnancies, 
bearing  triplets  twice,  twins  twice,  and  single 
young  four  times.  The  triplets  were  two  females 
and  a  male,  the  former  probably  free-martins. 
The  male  closeh'  resembled  the  mother,  while  the 
females  were  of  different  colour  and  pattern  like  the 
father. 

That  there  are  two  types  of  twins — identical  or 
uniovular,  of  the  same  sex,  and  showing  exceptionally 
close  resemblance;  and  biovular  or  fraternal,  show- 
ing  no  greater  resemblance  than  ordinary  brothers 
and  sisters — has,  of  course,  long  been  recognised. 
Occasionally  attempts  have  been  made  to  show  that 
twins  do  not  fall  into  such  categories,  but  without 
success.  Fisher  (191 9),  from  a  mathematical  treat- 
ment of  some  earlv  data  of  Thorndike,  thinks  it 
necessary  to  conclude  that  differences  in  the  degree 
of  resemblance  between  twins  could  be  accounted 
for  by  assuming  that  the  egg  divides  into  two 
halves,  each  of  which  is  fertilised  by  a  different 
spermatozoon.  vSuch  an  hypothesis  seems  to  have 
no  biological  or  experimental  evidence  in  its  favour, 
while  the  evidence  for  the  existence  of  both  biovular 


THE  LIMITS  OF  HEREDITY  199 

and  uniovular  twins  in  mankind  is  strong  and  un- 
equivocal.* 

It  was  formerly  supposed  that  identical  twins  were 
produced  by  separation  of  the  first  two  cells  formed  by 
the  division  of  the  fertilised  egg,  the  first  two  cells  into 
which  the  egg  divides  becoming  separated  after  the  egg 
has  been  fertilised  by  a  single  sperm.  There  is  experi- 
mental evidence  of  the  production  of  two  embryos 
or  of  double  monsters  from  invertebrate  eggs  by  this 
method.  But  since  the  investigations  of  Newman 
and  Patterson  on  the  armadillo,  in  which  the  latter 
showed  that  the  four  embryos  at  a  birth  are  produced 
by  budding  at  an  early  stage  of  development,  it  has 
seemed  much  more  probable  that  identical  twins 
(surrounded  by  a  common  chorion)  in  man  are  pro- 
duced in  a  similar  way.  Moreover,  the  number  of 
buds  in  the  nine-banded  armadillo  is  occasionally 
three  or  five,  and  varies  more  widely  in  other  species ; 
and  probabl}^  in  man  also  the  number  is  not  abso- 
lutely fixed,  but  may  occasionally  be  three,  thus 
accounting  for  some  cases  of  triplets  of  the  same  sex. 

Zeleny  (1921)  finds  a  definite  relation  between  the 
number  of  twin  births  and  triplet  births  in  mankind. 

Thus,   if  -    is   the  number  of  twin  births,  then  the 
n 

number  of  triplet  births  will  very  nearly  approximate 
2-      In     Prussia    during     the     years     1826-49     the 

ft' 

*  A  recent  case  (Arey,  1921)  proves  directly  the  origin  of 
identical  twins  from  a  single  ovum.  Twin  embryos  are  described, 
each  12*3  mm.  long,  and  contained  in  a  single  amnion  and  chorion. 
The  two  umbilical  cords  and  yolk-stalks  were  inserted  in  a  common 
yolk-sac.  In  a  second  pair  of  monochorionic  twin  embryos  with 
separate  amnions,  one  of  the  embryos  had  neither  yolk-stalk  nor 
sac.  It  is  suggested  that  the  human  embryo  probably  shows 
rather  rigid  determinate  cleavage,  and  that  monozygotic  or 
identical  twins  result  not  from  the  separation  of  blastomeres  or 
blastomere  clusters  in  early  cleavage,  but  "  from  later  fission  of 
the  inner  cell  mass." 


200  HEREDITY  AND  EUGENICS 

number  of  births  was  13,360,557.  The  frequency  of 
twin  births  was  i  in  89-1,  and  of  triplets  i  in  (88-9)^. 
For  quadruplets,  however,  there  is  an  excess  over 
expectation,  the  number  being  i  in  (71 -9)^.  Again, 
in  the  United  States  birth-registration  area  in  191 7 
the  number  of  births  is  recorded  as  1,339,975,  the 
number  of  twins  being  i  in  93-1,  and  of  triplets  i  in 
(93-0)2.  From  these  statistical  relations  it  would 
follow  that  "  triplets  are  produced  by  the  coincidence 
of  two  independent  processes  occurring  with  equal 
frequencies."  One  of  these  processes  gives  rise  to 
twins.  This  relation  w^ould  hold  whether  multiple 
births  occurred  through  multiple  ovulation  or  budding 
of  a  monoz3^gotic  embryo  or  both,  provided  that  each 
followed  the  rule.  This  result  is  remarkable  when 
one  considers  the  number  of  conditions,  both  bio- 
logical and  human,  which  contribute  to  produce  the 
registration  statistics. 

Man  appears  to  be  unique  among  animals,  as 
Davenport  points  out,  in  that  he  produces  both  types 
of  multiple  births:  (i)  by  the  budding  method  found 
in  the  armadillo;  (2)  multiple  births  from  separate 
eggs,  as  found  in  carnivora,  herbivora,  and  rodentia 
generally.  Differences  in  the  degree  of  resemblance 
betw^een  identical  twins  may  depend  in  part  on  the 
stage  at  which  budding  of  the  original  embryo  takes 
place.  Much  more  information  is  required  regard- 
ing human  multiple  births,  particular^  data  from 
obstetricians  on  such  matters  as  the  number  of 
chorions  present,  the  presence  of  blighted  embryos 
in  the  afterbirth,  and  the  relation  between  the  number 
of  corpora  lutea  and  the  number  of  embr3^os  at  a 
birth.  The  study  of  twins  presents  many  sides, 
and  will  furnish  evidence  on  a  variety  of  questions 
connected  with  heredit}^  and  reproduction  in  the 
human  race. 

The  recent   study  of   the  so-called  free-martin  or 


THE  LIMITS  OF  HEREDITY  201 

sterile  female  in  cattle  has  thrown  a  good  deal  of 
light  on  questions  of  sex  alteration,  and  also  on  the 
production  of  twins  in  cattle.  John  Hunter  (1779), 
in  an  early  account  of  the  free-martin,  states  that  it 
was  a  type  well  recognised  b}^  the  farmers  at  that 
time.  Such  barren  cows  in  Roman  times  were  called 
taurce,  but  apparently  the  Romans  did  not  understand 
the  manner  of  their  production.  Hunter  says:  '*  It 
is  a  known  fact,  and,  I  believe,  is  understood  to  be 
universal,  that  when  a  cow  brings  forth  two  calves, 
and  that  one  of  them  is  a  bull-calf,  and  the  other  a 
cow  to  appearance,  the  cow-calf  is  unfit  for  pro- 
pagation; but  the  bull-calf  becomes  a  very  proper 
bull."  This  clearly  states  the  general  facts  regarding 
the  production  of  free-martins.  Hunter  dissected 
three  such  animals  and  considered  them  hermaphro- 
dites, but  found  that  they  differed  from  one  another. 
He  gives  the  anatomical  details  of  his  dissections, 
and  states  that  free-martins  are  "  much  larger  than 
either  the  bull  or  the  cow,  and  the  horns  grow  longer, 
being  very  similar  to  the  horns  of  an  ox." 

The  important  investigations  of  Lillie  (191 7)  on  the 
foetal  development  of  twins  in  cattle  has  furnished 
a  clear  explanation  of  the  fact  that  the  free-martin 
is  nearh^  always  sterile.  The  internal  reproductive 
organs  of  the  free-martin  are  found  to  be  usually 
predominantly  male,  while  the  external  organs  are 
at  least  usually  female,  but  there  are  considerable 
variations.  Lillie 's  main  disco verv  was  that  in  the 
production  of  twin  embryo  cattle  there  is  a  secondary 
fusion  of  the  two  chorions  and  anastomosis  of  the 
circulation  of  the  two  foetuses.  The  free-martin  is  a 
female  transformed  by  the  action  of  hormones  derived 
from  the  male  twin,  which  pass  through  the  anasto- 
mosed bloodvessels  into  the  circulation  of  the  female 
embryo.  Nearl}-  all  twins  of  cattle  are  monochorial, 
with    the    chorions    more    or    less    completely    fused. 


202  HEREDITY  AND  EUGENICS 

About  1 3  per  cent,  of  free-martins  (z.^., females  twinned 
with  a  male  calf)  are  fertile.  This  happens  when  the 
fusion  of  chorions  does  not  take  place,  and  there  is 
hence  no  opportunity  for  the  male  embryo  to  influence 
the  development  of  the  female.  It  is  also  found  that 
there  are  always  in  cattle  two  corpora  lutea  present 
when  twins  are  born,  and  a  single  one  at  single  births. 
This  shows  that  the  vast  majority,  at  least,  of  twins 
in  cattle  are  derived  from  two  separate  eggs.  There 
is  no  certain  evidence  that  monozygotic  twins  ever 
occur  in  cattle.  This  is  contrary  to  the  condition  in 
man,  where  both  monozygotic  (identical)  and  dizygotic 
(fraternal)  twins  are  now  known  to  occur. 

That  monozygotic  twins  occur  but  rarel}',  if  at  all, 
in  cattle  and  sheep,  is  shown  b}^  the  ratio  of  the  sexes 
in  twin  births.  This  ratio  closel}^  approximates 
ic?c^:2?c^:i$  ?,  which  would  occur  if  all  tw^ins  were 
derived  from  separate  ova.  The  data  on  this  subject 
have  been  considered  by  Go  wen  (1922).  In  human 
twin  births  there  is  a  wide  departure  from  this  ratio, 
owing  to  the  occurrence  of  "  identical  "  twins  derived 
from  a  single  ovum.  Thus,  in  statistical  records  of 
Nichols,  the  proportions  of  the  sexes  in  human  twin 
births  is  males,  234,497;  male  and  female,  264,098; 
females,  219,312.  This  represents  a  ratio  of 
I  -07  :  I  -20  :  I .  These  statistics  are  clearly  in  harmony 
with  the  view^  that  both  uniovular  and  biovular  twins 
occur  in  man. 

Gowen  has  also  compared  the  colour  markings  of 
cattle  twins,  taken  from  the  Herd  Books  of  the 
American  Jersey  Cattle  Association.  These  records 
included  749  twin  females,  168  twin  males,  and  207 
male  and  female.  Compared  as  regards  colour  mark- 
ings, tongue  colour,  and  switch  colour,  there  was  found 
to  be  little  if  any  significantly  greater  resemblance 
in  favour  of  twins  of  like  sex.  There  w^as,  however, 
5    per   cent,   greater  resemblance   in  favour  of  male 


THE  LIMITS  OF  HEREDITY  203 

twins  as  compared  with  twins  which  are  male  and 
female,  and  this  might  be  due  to  the  occurrence  of 
monozygotic  twins.  But  in  no  case  is  this  difference 
greater  than  twice  the  probable  error,  so  it  really 
furnishes  no  eyidence  in  fay  our  of  the  occurrence  of 
monozygotic  twins  in  cattle. 

Lush  (1922)  describes  a  pair  of  twin  Jersey  heifers 
which  he  thinks  are  identical.  They  both  haye  a 
moderate  notch  (see  p.  135)  in  their  ears;  their  noses, 
tongues,  switches,  and  general  shade  of  body  colour 
are  the  same;  and  they  each  haye  a  single  spot  on 
the  right  hind  foot.  This  indicates  that  monozygotic 
twins  occasionally  occur  in  cattle.  It  is  hardly 
likely  that  both  parents  would  be  homozygous  for 
all  these  characters. 

In  pigeons,  two  pairs  of  female  monozygotic  twins 
haye  been  described  (Riddle,  191 8).  They  were  both 
deriyed  from  eggs  with  yery  large  yolks,  but  not 
"  double-yolked,"  the  embryos  haying  a  single  3^olk 
sac.  It  is  belieyed  that  they  were  formed  by  the 
separation  of  the  first  two  blastomeres  in  the  fertilised 
egg,  this  separation  being  a  result  of  the  yery  large 
initial  size  of  the  e.gg. 


CHAPTER  VI 

SOCIAL  AND  WORLD  ASPECTS  OF 

EUGENICS 

While  the  observation  and  study  of  the  innumerable 
alternative  differences  in  man  is  a  theme  of  great 
interest,  yet  it  lies  for  the  most  part  outside  the  range 
of  practical  eugenics,  for  great  numbers  of  these 
differences,  aside  from  abnormalities,  are,  as  far  as 
our  present  knowledge  goes,  innocuous  in  nature, 
being  neither  advantageous  nor  detrimental  in  their 
effects,  but  lending  a  pleasing  and  desirable  variety 
to  the  huinan  race.  The  aim  of  practical  eugenists 
would,  then,  be  rather  so  to  direct  selection  by  con- 
trolling the  conditions  w^hich  determine  selection 
as  to  eliminate  the  obviously  undesirable  or  anti- 
social traits ;  and  to  improve,  through  public  opinion 
or  otherwise,  the  chances  of  perpetuation  and  in- 
crease of  their  kind  on  the  part  of  the  better  qualified 
members  in  every  stratum  of  society.  This  aim, 
though  easily  stated,  is  obviously  almost  infinitely 
difficult  of  achievement  in  a  complex  civilisation. 
And  it  is  rendered  all  the  more  difficult  by  the  fact 
that  eugenics  aims,  not  to  establish  and  improve  a 
single  type,  as  in  breeding,  for  example,  racehorses, 
but  at  the  infinitely  more  complex  result  of  improv- 
ing innumerable  more  or  less  inter-breeding  strains 
simultaneously,  weeding  out  their  more  defective 
members  or  qualities,  and  at  the  same  time  main- 
taining the  diversity  of  t3^pes  in  the  whole  population. 
A  world  of  Shakespeares  or  Newtons  or  Goliaths, 
even  if  attainable,  would  not  be  an  econgmic  success. 

204 


SOCIAL  AND  WORLD  ASPECTS  205 

Differentiation  of  types  is  one  measure  of  civilisation, 
and  no  high  type  of  culture  could  long  be  maintained 
without  it.  The  miner  and  the  professor,  the  peasant 
and  the  banker,  each  in  his  sphere  makes  his  contri- 
bution to  civilisation,  and  so  widens  its  boundaries 
and  increases  the  richness  (mentally  and  morally,  as 
w^ell  as  economically)  of  the  social  inheritance  of 
tradition  which  makes  the  maintenance  of  culture 
possible  and  the  development  of  culture  cumulative. 

Nevertheless,  there  is  great  need  for  improvement 
in  the  general  mental  and  ph3^sical  level  of  our  race 
through  some  form  of  selection.  Probabl}"  no  race 
has  ever  rivalled  the  Greeks  in  the  number  of  great 
men  they  produced  in  a  relatively  small  population 
during  a  period  of  a  few  centuries.  It  should  be 
possible  to  devise  some  more  effective  means  of 
discovering  the  youths  of  exceptional  quality  in 
every  stratum  of  societ}',  and  giving  them  larger 
opportunities  of  self-expression.  Mere  advocacy  of 
an  indiscriminately  higher  birth-rate,  fostered  by 
artificial  doles  to  the  poorer  classes  of  society,  \wi\\ 
only  achieve  a  dysgenic  result.  An  able  discussion 
of  these  problems  is  to  be  found  in  Bateson's  presi- 
dential address  to  the  British  Association  in  Sydney, 
Australia,  1914. 

The  presence  of  various  pairs  of  alternative 
characters  in  the  same  individual  probably  has  the 
same  stimulating  effect  in  man  that  it  has  been 
experimentally  shown  to  have  in  such  organisms  as 
maize  and  wheat.  The  frequently  increased  vigour 
of  hybrids  was  known  to  Darwin  and  other  early 
writers,  but  modern  genetic  experiments  have  given 
the  facts  a  much  more  precise  orientation,  although 
its  cause  cannot  yet  be  said  to  be  fully  understood. 
The  phenomenal  growth  of  certain  hybrid  walnuts, 
and  the  remarkable  hardiness  and  vigour  of  such 
hybrid  trees  as  the   London  plane,  are  well  known. 


2o6  HEREDITY  AND  EUGENICS 

But,  on  the  other  hand,  inbreeding  by  no  means 
necessaril}^  leads  to  deterioration.  Among  plants, 
garden  beans  (Phaseolus  vulgaris)  and  the  small- 
flowered  evening  primroses  (of  which  there  are  many 
species)  are  regularly  self-pollinated,  and  probably 
are  crossed  only  at  long  intervals  under  exceptional 
circumstances.  Yet  they  are  not  lacking  in  vigour, 
and,  indeed,  the  small-flowered  (Enotheras  are  much 
more  widespread  in  their  wild  condition  in  North 
America  than  the  large-flowered  forms  which  are 
open-pollinated,  and  hence  give  greater  chances  for 
crossing.  The  former  have  been  more  successful  in 
an  evolutionar}-  w^ay,  despite  their  self-pollination. 
The  advantages  of  ensured  seed  production  for 
every  flower  have  more  than  counterbalanced  any 
advantages  derived  from  crossing. 

In  this  connection  it  is  necessary  to  remember 
several  points.  First,  the  h^^brid  vigour  or  heterosis 
arising  from  crossing  both  in  plants  and  in  animals 
is  confined  very  largely,  or  in  some  cases  entirely,  to 
the  first  hybrid  generation.  It  is  therefore  a  purety 
temporary  phenomenon,  unless  the  crossing  is  con- 
tinued in  each  generation.  It  is  apparently  not  even 
a  constant  accompaniment  of  the  heteroz3^gous  con- 
dition, but  is  speciall}^  characteristic  of  the  F^ 
generation.  Another  point  to  remember  is  that  in- 
breeding, which  must  always  occur  to  some  extent 
even  amongst  wild  animal  species,  tends  to  reduce 
the  amount  of  heterozygosity  in  each  generation. 
Probably  in  man,  in  whom  a  host  of  character- 
differences  are  being  redistributed  in  each  generation, 
a  homoz3^gous  condition  is  seldom  reached,  except  as 
regards  a  relatively  small  number  of  characters. 
The  degree  to  which  the  homozygous  condition  exists 
in  any  family  may  be  to  some  extent  measured  by 
the  amount  of  diversity  between  sibs  (brothers  and 
sisters)  and  their  parents,  grandparents,  and  collateral 


SOCIAL  AND  WORLD  ASPECTS  207 

relations.  Obviously,  if  they  all  resemble  each  other 
in  a  particular  character,  the  family  will  be  homozygous 
for  that  character.  But  it  appears  that  in  inodern 
civilised  races,  at  any  rate,  this  is  seldom  the  case, 
even  for  a  single  character.  Nevertheless,  many 
Scandinavian  families  are  probably  homozygous  for 
blue  e^^es,  and  other  similar  cases  might  be  mentioned, 
but  they  are  obviously  exceptional.  This  brings  us 
to  consider  briefly  some  of  the  mathematical  laws 
connected  with  in-breeding  and  cross-breeding. 

A  considerable  mathematics  has  grown  up  about 
the  stud}'  of  Mendelian  characters.  It  is  not  my 
purpose  to  deal  with  that  literature  here,  but  a  few 
of  the  consequences  of  Mendelian  inheritance  as 
regards  the  whole  population  may  be  pointed  out. 
There  is  considerable  evidence  that  man}'  trivial 
characters  in  plants  and  animals,  as  well  as  in  man, 
are  quite  innocuous  as  regards  the  welfare  of  the 
organism,  at  least  under  usual  conditions.  It  is 
difficult  to  believe  that  a  long  nose  or  blue  eyes  is  of 
an}^  direct  biological  advantage  to  their  possessor 
in  a  civilised  communit}^  in  temperate  countries. 
But  under  a  burning  sun  in  a  condition  of  nature 
it  is  at  least  highly  probable  that  a  pigmented  iris 
as  well  as  a  pigmented  skin  are  a  distinct  protection. 
This  is,  perhaps,  why  such  mutations  in  loss  of  pig- 
mentation as  have  occurred  to  native  races  in  the 
tropics,  have  never  been  able  to  establish  themselves 
or  give  rise  to  a  distinct  type. 

While  natural  selection  as  regards  blue  or  brown 
eye  colour  is  therefore  probabl}'  inoperative  in 
temperate  countries,*  it  might  easity  become  opera- 
tive under  wild  conditions  in  the  tropics.  W^arren 
(191  7),  in  a  paper  on  the  numerical  effects  of  natural 
selection  acting  upon  Mendelian  characters,  shows 
the  number  of  generations  which  would  be  required 

*  What  sexual  selection  may  do  is  another  matter. 


2o8  HEREDITY  AND  EUGENICS 

to  eliminate  a  dominant  or  a  recessive  character. 
He  finds  that  in  a  Mendehan  population  in  which  the 
numbers  tend  to  double  in  each  generation,  and  in 
which  a  dominant  character  has  twice  the  viability 
of  the  corresponding  recessive,  then  the  recessive  will 
be  eliminated  in  the  eleventh  generation.  On  the 
other  hand,  if  the  recessive  is  twice  as  viable  as  the 
dominant,  then  the  latter  will  be  eliminated  in  eight 
generations.  Hence,  other  things  being  equal,  the 
elimination  of  a  deleterious  dominant  character  is 
more  rapid  than  of  a  recessive. 

The  subject  of  the  Mendelian  proportions  in  a 
mixed  population  was  first  considered  by  Pearson 
(1904).  He  showed  that  with  random  mating  of  two 
forms  A  A  and  a  a  and  their  progen}^,  the  formula 
AA -\- 2 Ka-\- 2 aa  will  apply  to  the  proportions  in  every 
later  generation — i.e.,  the  population  will  remain 
stable.  Hard}^  (1908)  pointed  out  the  same  thing. 
Pearl  (191 3,  1914)  has  worked  out  formulae  for  differ- 
ent types  of  inbreeding,  and  determined  coefiicients 
for  different  degrees  of  relationship  among  inbred 
pedigrees.  Jennings  (191 6)  has  elaborated  eight}"- 
two  formulae,  from  which  can  be  calculated,  in  many 
cases  directly,  the  results  of  various  systems  of 
breeding  in  a  Mendelian  population.  The  results 
vary,  of  course,  not  only  according  to  the  system  of 
breeding  followed,  but  also  according  to  the  com- 
position of  the  population  at  the  beginning.  The 
systems  of  breeding  analysed  include  random  mating, 
assortative  mating,  self- fertilisation,  and  various 
systems  of  inbreeding,  and  from  the  formulae  obtained 
the  relative  proportions  of  the  various  t3^pes  in  any 
generation  may  be  determined. 

With  random  mating  the  resulting  population 
generally  remains  stable,  but  with  inbreeding  or 
assortative  mating  it  may  alter  progressively  in  a  given 
direction.     Inbreeding  wall  also,  of  course,  gradually 


SOCIAL  AND  WORLD  ASPECTS  209 

transform  any  heteroz3"gous  population  into  a  homo- 
zygous one,  the  rapidity  with  which  the  completel}' 
homozygous  condition  is  reached  depending  on  the 
system  of  inbreeding  employed  and  the  degree  of 
heterozygosity  in  the  original  population.  Self- fertili- 
sation, which  is  not  uncommon  in  plants,  is,  of  course, 
the  most  stringent  form  of  inbreeding,  and  it  quickly 
reduces  any  heterogeneous  heterozygous  population 
to  a  completely  homoz^'gous  (but  heterogeneous)  con- 
dition, unless  some  condition  in  the  germ  plasm,  such 
as  balanced  lethal  factors,  or  some  method  of  repro- 
duction, such  as  apogamy.  prevents  the  gametic 
representatives  of  the  different  characters  being  freel}' 
redistributed  to  the  next  generation.  In  wild  species, 
also,  some  of  the  Mendelian  characters  in  the  popula- 
tion may  be  subject  to  natural  selection,  positiveh' 
or  negatively,  and  thus  alter  their  proportions  in  the 
population.  This  would  lead  to  the  elimination  of 
certain  characters,  even  in  a  population  mating  at 
random,  although  such  characters  are  more  dithcult 
to  eliminate  from  the  germ  plasm  when  recessive  than 
when  dominant.  In  the  same  way  the  action  of 
natural  selection  would  lead  to  the  more  rapid 
multiplication  and  spread  in  the  population  of  a 
favoured  character  whether  dominant  or  recessive. 

Laughlin  (1920)  has  worked  out  the  conditions  of 
ancestral  inheritance  in  man,  assuming  twelve  pairs 
of  chromosomes  representing  as  man}^  pairs  of  linked 
genes.  Galton's  original  law  of  ancestral  inheritance 
is  well  known — namely,  that  the  two  parents  con- 
tribute 50  per  cent.  (0-5)  of  the  inheritance,  the  four 
grandparents  25  per  cent,  or  (0-5)^,  the  eight  great- 
grandparents  12*5  per  cent  (0-5)^,  etc.,  the  total 
heritage  being  (0-5) +(0-5)^ +  (0-5)^+ .  .  .  =  1.  Karl 
Pearson  later  modified  this  scheme,  on  the  basis 
of  statistical  data  of  correlation  between  father  and 
son,  finding  that  the  resemblance  varied  from  30  per 


2IO  HEREDITY  AND  EUGENICS 

cent,  or  more  for  some  characters  to  50  per  cent, 
or  more  for  others.  Laughhn's  scheme  is  based  upon 
the  known  constitution  of  the  germ  plasm — i.e.,  its 
division  into  chromosomes,  each  bearing  its  group  of 
genes ;  and  ancestral  influence  is  measured  by  tracing 
individual  chromosomes  backwards  through  previous 
generations.  The  "  trail  "  of  a  given  chromosome 
in  the  ascendant  or  descendant  generations  will  depend 
upon  the  laws  of  probability  and  recombination,  and 
these  laws  will  differ  for  the  ordinary  chromosomes 
and  the  X  and  Y  chromosomes.  On  this  basis  various 
mathematical  formulae  are  developed  for  calculating 
ancestral  influence. 

The  Basis  of  Racial  and  Temperamental 

Differences. 

In  discussing  questions  of  elimination  or  increase 
of  certain  types  or  characters,  it  is  very  desirable  to 
know  not  only  what  relation  these  characters  bear 
to  the  economy  of  the  organism,  but  also  what  are 
their  sources  and  controls  in  its  development.  The 
ductless  or  endocrine  glands,  which  have  been  studied 
in  recent  3^ears,  are  of  the  utmost  importance  in  this 
connection.  The}'  pour  direct h'  into  the  blood  in 
minute  quantities  hormones  which  influence  and  con- 
trol directly  the  activities  of  various  organs  of  the 
body.  They  also  form  a  system  of  checks  and 
counterchecks  to  each  other,  and  so  constitute  a 
sort  of  interlocking  directorate,  exercising  the  most 
complete  control  over  the  bodily  activities,  as  a  whole, 
through  the  medium  of  the  substances  they  discharge 
in  minute  traces  into  the  blood.  These  glands  have 
a  very  long  evolutionary  history,  being  derived 
from  totalh^  different  organs  having  other  functions, 
which  are  present  in  the  lower  vertebrates  (Chordates) 
such  as  Amphioxus . 

In  his  presidential  address  to  the  Anthropological 


SOCIAL  AND  WORLD  ASPECTS  211 

Section  of  the  British  Association,  Sir  Arthur  Keith 
(1920)  discusses  the  basis  of  differentiation  of  man- 
kind into  racial  types,  and  shows  how  the  character- 
istic racial  differences  are  probably  connected  with 
differences  in  the  secretions  of  the  endocrine  glands. 
He  points  out  that  the  characteristic  differences  of 
feature,  build,  and  colour  cannot  (for  the  most  part) 
have  been  evolved  directh^  by  natural  selection  of 
variations,  and  elaborates  the  view  that  the  differences 
observed  are  a  result  of  variations  which  have  arisen 
in  the  organs  of  internal  secretion.  These  glands  are 
now  known  to  control  in  a  marvellous  manner  the 
processes  of  development  and  functioning  of  the  body. 
The  principal  of  these  organs  are  as  follow^s :  (i)  The 
thyroid  (a  gland  in  the  neck,  astride  the  trachea); 
(2)  the  parathyroids  (four  small  glands  close  to  the 
thyroids);  (3)  the  pituitary  (a  small  reddish  organ  at 
the  base  of  the  skull),  of  which  the  anterior  and 
posterior  lobes  have  different  functions ;  (4)  the  pineal 
body;*  (5)  the  suprarenal  capsules,  over  the  kidney's, 
consisting  of  cortex  and  medulla,  with  different  origins 
and  diverse  functions ;  (6)  the  islets  of  Langerhans 
in  the  pancreas  ;  (7)  the  interstitial  tissue  of  the  gonads . 
These  glands  pour  directly  into  the  blood  which 
bathes  them  extremely  minute  quantities  of  their 
various  secretions,  and  the  latter  control  in  remark- 
able fashion  both  the  development  and  functioning, 
not  only  of  the  body,  but  also  to  some  extent  of  the 
brain  and  mind. 

The  first  instance  in  which  the  form  of  the  body 
was  found  to  be  influenced  by  an  internal  secretion 
was  that  in  which  a  pathological  condition  of  the 
pituitar}^  was  shown  to  be  the  cause  of  the  condition, 
known  as  acromegaly,  in  which  there  is  enlargement 
of  the  bones  and  flesh  of  the  hands,  feet,  and  face. 

*  A  small  gland,  about  the  size  of  a  pea,  under  the  brain, 
resting  on  the  anterior  corpora  quadrigemina. 


212  HEREDITY  AND  EUGENICS 

Enlargement  of  the  pituitary  is  also  frequently 
associated  with  gigantism.  Dwarfism  may  result 
from  an  invasion  of  the  pituitary  by  tumours,  and 
also  from  a  failure  of  functioning  on  the  part  of  the 
thyroid.  If  such  conditions  are  induced  by  deranged 
functioning  of  these  glands,  it  is  reasonable  to  suppose 
that  corresponding  racial  (inherited)  differences  would 
arise  from  germinal  changes,  w^hose  effect  is  to  alter 
the  cjuantity  (or  quality)  of  these  secretions.  The 
Caucasian,*  according  to  Keith,  shows  a  greater  pre- 
dominance of  the  pituitary  than  the  Negro  or  Mongol, 
as  indicated  by  the  pronounced  nasalisation  of  the 
face,  the  tendency  to  strong  eyebrow  ridges,  prom- 
inent chin,  and  the  tendenc}^  to  greater  stature 
and  bulk  of  body.  It  is  also  suggested  that  the 
beardless  face  and  almost  hairless  body  of  the  repre- 
sentative Negro  and  Mongol  types  is  due  to  a  lesser 
activity  of  the  interstitial  glands,  the  long  stork-like 
legs  of  Nilotic  and  other  tribes  resulting  from  a  greater 
abeyance  of  the  same  glands. 

In  the  same  way,  differences  in  the  pigmentation 
of  the  skin,  which  characterise  the  various  races  of 
mankind,  may  be  reasonably  assumed  to  be  due  to 
inherited  differences  in  the  activities  of  the  suprarenal 
bodies,  since  it  is  known  that  Addison's  disease,  in 
which,  among  other  symptoms,  there  is  a  darkening 
of  the  skin  through  pigmentation,  is  the  result  of  a 
pathological  condition  of  the  adrenal  cortex.  Thus, 
the  great  colour  varieties  of  mankind  are  probably 
determined  in  part  by  differences  in  the  activity  of 
the   adrenal   bodies ;   but    it    is    probable   that    other 

*  Of  course,  anthropologists  now  recognise  that  there  is  no 
Caucasian  race,  but  that  modern  European  populations  are  a 
mixture  in  various  proportions  of  three  distinct  races:  (i)  Nordic 
tall,  blue-eyed,  and  long-headed  (dolichocephalic);  (2)  Alpine, 
short  and  stocky,  brown-eyed  and  broad-headed  (brachycephalic) ; 
(3)  Mediterranean,  small  and  slender,  brown-eyed  and  long- 
headed. 


SOCIAL  AND  WORLD  ASPECTS  213 

glands  as  well  are  concerned  in  the  determination  of 
skin  pigmentation,  and  we  have  already  indicated 
some  of  the  other  racial  differences  which  they 
probably  control  as  well.  If,  then,  in  the  various 
races  hereditary  differences  in  the  activities  of  these 
glands  of  internal  secretion  are  concerned,  it  may  be 
expected  that  the  results  of  racial  crosses  will  be 
very  different  from  what  they  would  be  if  there  were 
direct  determiners  for  the  various  individual  visible 
characters.  For  each  endocrine  (ductless)  gland 
has  various  activities  and  affects  the  development  oi 
many  parts  of  the  body.  In  crosses  between  races, 
whole  complexes  of  characters  w^ould  then  be  ex- 
pected to  be  inherited  or  modified  together.  If  the 
difference  between  a  white  and  a  black  skin  is  due  to 
the  greater  activity  of  the  suprarenals  in  the  white 
race,  then  it  would  appear  that  quantitative  differences 
in  the  activities  of  these  organs  are  the  units  really 
involved  in  white-black  crosses.  The  laws  of  quan- 
titative inheritance  are  by  no  means  clearl}^  under- 
stood at  the  present  time,  nor  are  even  the  facts  of 
colour  inheritance  in  mankind  entirely  agreed  upon 
(see  p.  52) ;  but  if  they  are  due  to  inherited  differences 
in  endocrine  activitv,  we  have  here  the  basis  for  a 
further  analysis  and  understanding  of  the  combined 
phenomena  of  blending  and  segregation  in  the  colour 
inheritance  of  racial  crosses. 

The  thyroid  is  considered  by  Keith  to  be  anthro- 
pologically the  most  important  of  all  the  endocrine 
glands.  The  thyroid,  like  all  these  glands,  is  believed 
to  throw  off  two  types  of  substances,*  one  which  is 

*  It  may  be  questioned  whether  there  are  really  two  types  of 
substances  given  off,  one  early  in  development  and  the  other 
after  maturity.  It  appears  rather  that  a  germinal  change  in,  for 
example,  thyroid  production  causes  morphogenetic  changes 
which  will  be  inherited,  while  a  functional  derangement  of  the 
same  kind  occurring  later  will  produce  different  results  and  not 
be  inherited. 


214  HEREDITY  AND  EUGENICS 

morphogenetic  and  affects  the  development,  the  other 
which  controls  and  regulates  in  a  remarkable  manner 
various  activities  of  the  body  through  the  minute 
traces  of  certain  substances  which  it  pours  into  the 
blood.  This  latter  substance  in  the  case  of  th3'roid 
is  known  as  thyroxin.  It  has  been  isolated  and  its 
chemical  structure  determined,  the  molecule  being 
found  to  contain  iodine  and  arsenic.  About  150 
grains  were  obtained  from  some  6,000  pounds  of  ox 
thyroid,  so  that  the  amount  of  thyroxin  poured  daih' 
into  the  blood  of  a  man  must  be  almost  too  infini- 
tesimal for  computation.  The  condition  known  as 
myxcedema,  which  is  accompanied  by  peculiarities  of 
the  skin  and  hair,  disappears  when  thyroid  extract 
is  administered.  Berman  (1921)  cites  the  fact  that, 
as  early  as  1891,  sheep  th3^roid  was  administered  to  a 
woman  with  myxcedema.*  The  symptoms  disap- 
peared, but  she  was  obliged  to  continue  taking  thyroid 
extract  until  her  death,  in  191 9.  In  this  period  of 
twenty-eight  years  she  consumed  nine  pints  of 
thyroid,  equivalent  to  the  extract  from  the  glands 
of  870  sheep. 

Hence,  the  thyroid  acts  directly  on  the  skin  and 
hair,  which  are  the  chief  structures  used  in  the  classi- 
fication of  the  races  of  mankind.  It  also  affects  the 
skeleton,  and  when  deficient,  causes,  according  to 
Keith,  arrested  development  of  the  basal  part  of  the 
skull,  the  root  of  the  nose  appearing  to  be  flattened 
and  drawn  backw^ards  between  the  eyes,  the  upper 
forehead  projecting  or  bulging,  the  face  being  flattened, 
and  the  bony  scaffolding  of  the  nose  greatly  reduced. 
These  are  all  characteristic  features  of  the  Mongohan 

*  A  condition  with  dropsy-like  swelling  caused  by  failure  of 
nutrition  from  defective  nerve  influence.  It  is  associated  with 
atrophy  of  the  thyroid,  and  is  probably  directly  due  to  excess 
of  mucin  in  the  system.  It  is  accompanied  by  sluggish  move- 
ments, thick  speech,  and  dull  mental  condition. 


SOCIAL  AND  WORLD  ASPECTS  215 

face,  and  to  a  lesser  degree  of  the  Negro  face.  Hence, 
it  is  concluded  that  a  reduction  or  alteration  in  th^Toid 
activity  has  been  a  factor  in  determining  some  of  the 
characteristics  of  these  races.  The  Mongol  might  be 
characterised  as  subthyroid  relatively  to  the  white 
man,  while  the  negro  is  relatively  subadrenal. 
Similarly  such  Eastern  races  as  the  Malays,  Siamese, 
Chinese,  and  Japanese,  having  nearl}^  hairless  faces 
and  little  hair  on  their  bodies,  may  be  classed  as 
in  some  respects  eunuchoid,  with  a  weak  secretion 
from  the  adrenal  cortex.  They  are,  however,  vigorous 
and  prolific,  and  these  are  not  eunuchoid  charac- 
teristics. The  social  dominance  of  the  white  man 
might,  then,  be  said  to  be  due  to  the  greater  concen- 
tration of  certain  hormones  in  his  blood. 

Achondroplasia  (see  pp.  34,  39)  is  a  form  of  dwarfing 
due  to  hypothyroidism,  and  is  inherited.  In  man  it 
may  be  accompanied  by  shortening  of  the  face 
(prosopia),  as  in  the  bull-dog,  or  the  face  may  be 
unaffected,  as  also  in  the  dachshund.  The  latter 
condition  is  much  less  common.  Short  limbs  and  a 
long  trunk,  accompanied  by  retraction  of  the  nasal 
region  of  the  face,  are  all,  according  to  Keith, 
Mongolian  characteristics.  The  so-called  ^Mongolian 
idiots  (see  p.  152)  are  stunted  individuals,  imbeciles 
with  Mongoloid  features.  Their  occurrence  among 
Caucasian  offspring  is  not  an  indication  of  ^longol 
ancestr}^  outcropping,  but  is  a  form  of  hypothyroidism. 
On  the  other  hand,  enlargement  of  the  th3Toid  causes 
goitre,  and  there  are  particular  regions,  as  the  vicinity 
of  the  Great  Lakes  of  North  America,  where  goitre  is 
more  frequent  owing,  apparently,  to  insufficiency  of 
iodine  in  the  water.*  According  to  Berman  (1921),  the 
thyroid  also  controls  the  speed  of  living.     With  more 

*  There  is  some  evidence  that  goitre  is  concerned  with  a 
specific  bacillus,  one  host  of  which  is  the  goat,  and  that  it  may 
be  conveyed  by  contamination  of  drinking-water. 


21 6  HEREDITY  AND  EUGENICS 

thjToid  one  thinks  and  acts  more  quickly.  One 
milligram  of  th3'roxin  is  found  to  increase  the  rate  of 
metabolism  2  per  cent.  Cretin  babies  fed  on  th^-roid 
undergo  a  remarkable  mental  and  physical  transforma- 
tion to  normal  human  beings.  But  the}^  must  be  fed 
on  it  all  their  lives,  or  they  relapse  into  their  former 
condition,  because  they  are  incapable  of  producing 
the  secretion  themselves.  More  recently  Keith  (1922) 
has  elaborated  his  views  on  this  subject  in  an  extremely 
interesting  way,  discussing  such  subjects  as  the 
Neanderthal  skull,  acromegaly,  dwarfism,  and  many 
other  anatomical  alterations  from  the  point  of  view 
of  hormone  control. 

Seligman  (1904)  has  described  the  frequent  oc- 
currence of  "  cretins  "  in  Dexter  Kerry  cattle.  The 
breed  appears  to  have  originated,  at  Kerry  at  least, 
as  earh^  as  the  middle  of  the  eighteenth  centur3^ 
One  of  its  most  striking  features  is  the  very  short 
legs,  which  suggest  a  condition  of  h^'pothyroidism. 
In  one  herd  fourteen  cretins  were  produced  among 
fift^^-five  calves  in  seven  years.  Another  herd  pro- 
duced five  cretins  among  tw^ent\'-seven  calves  in  three 
3^ears.  These  "  bull-dog  monsters  "  are  non- viable, 
and  abnormal  in  man}^  respects.  Their  chief 
peculiarities  are  their  short  trunk  and  extremely 
dwarfed  limbs  (humerus  onl}^  1 3  millimetres  in  length), 
the  extreme  brachycephaly  of  the  head  with  its 
rounded  forehead  bulging  over  the  ver}'  depressed 
nose  and  upper  jaw,  while  the  lower  jaw  is  normally 
developed.  There  is  always  a  gap  in  the  abdominal 
wall  through  which  the  internal  organs  protrude. 
The  palate  is  cleft,  the  tongue  long  and  protruding, 
while  the  thyroid  is  irregularly  developed,  and  shows 
the  same  histological  peculiarities  as  the  thyroid  of 
cretin  children.  It  w^as  probably  devoid  of  proper 
secretion,  as  the  extract  of  such  glands  produced  little 
or  no  fall  in  blood  pressure  when  injected  intravenously. 


SOCIAL  AND  WORLD  ASPECTS  217 

This  condition  of  cretinism  is  said  to  be  constantly 
associated  with  placental  disease,  which  would  pre- 
vent the  thyroid  hormones  of  the  mother  from  acting 
properh'  upon  the  young.  The  frequent  occurrence 
of  cretinism  in  this  breed  of  cattle  may,  then,  perhaps 
be  accounted  for  by  a  diseased  placenta  preventing 
the  already  hypothyroid  mother  from  furnishing  her 
offspring  with  sufficient  thyroid  secretion.  There  is 
another  explanation,  however,  which  appears  more 
probable.  In  at  least  one  case  a  cow  is  known  to 
have  produced  a  normal  calf  following  a  cretinous 
one.  Any  defect  in  the  placenta  would  then  probably 
not  be  the  result  of  a  diseased  condition  of  the  cow, 
but  rather  the  initial  defect  would  be  in  the  developing 
foetus.  Another  fact  which  may  be  significant  is  the 
occurrence  of  25-4  per  cent,  of  "  cretinous  "  offspring 
in  the  larger  herd  already  referred  to.  This  clearly 
suggests  that  the  condition  is  a  Mendelian  recessive, 
due  to  a  lethal  mutation  carried  in  the  germ  plasm 
of  the  breed,  or  in  some  of  them.  Further  data  would 
be  required  in  order  to  verify  this  h^'pothesis. 

Sir  Arthur  Keith  applies  the  same  conceptions  of 
hormone  determination  to  the  anthropoid  apes  and 
other  vertebrates,  holding  that  in  the  orang  there  is  a 
predominance  of  thyroid,  while  in  the  gorilla  the 
pituitary  is  predominant.  However  this  may  be,  the 
view  seems  well  founded  that  raciiil  differences  in 
man,  including  the  colour  and  character  of  the  skhi 
and  hair,  differences  in  physiognomy  and  in  stature 
and  the  relative  length  of  limbs,  are  related  to  inherited 
differences  in  the  activities  of  various  endocrine 
glands.  This  thesis  will,  no  doubt,  be  further 
elaborated  with  increasing  knowledge. 

The  bodily  changes  associated  with  pain,  fear,  and 
rage  have  been  particularly  studied  by  Cannon  (191 6), 
who  showed  how  in  a  state  of  fear  or  anger  adrenahn 
is    poured    into    the   blood,    which    causes   reactions, 


21 8  HEREDITY  AND  EUGENICS 

putting  the  body  into  a  state  of  defence  in  the  most 
marvellous  wa\^  The  substance  adrenalin  is  derived 
from  the  medulla  of  the  adrenal  glands.  It  has  been 
chemically  synthesised,  and  Schaefer  showed  that 
when  injected  into  the  veins  it  raises  the  blood- 
pressure.  Its  concentration  in  the  blood  is  only  about 
I  part  in  20,000,000,  and  100,000  times  this  quantity 
is  held  in  the  gland  ready  for  emergencies.  Cannon 
showed  that  w-hen  secreted  into  the  blood,  as  a  result 
of  the  emotions  of  fear  or  anger,  it  prepares  the  body 
for  mortal  combat  by  summoning  its  reserves  and 
increasing  its  defences.  It  stimulates  the  liver  to  pour 
out  more  carbohydrates.  The  blood  is  thus  flooded 
with  sugar  which  can  immediately  be  used  as  fuel  for 
the  body  in  exertion.  The  number  of  red  corpuscles 
in  the  blood  is  also  increased,  the  blood  is  withdrawn 
from  the  skin  and  viscera  and  sent  to  the  muscles, 
heart,  lungs,  and  central  nervous  system.  The  limbs 
actually  grow  larger  wdth  their  increased  blood  suppl}^ 
the  heart  beats  faster,  and  the  senses  are  keener;  the 
effects  of  fatigue  are  abolished,  and  the  blood  is 
rendered  more  coagulable.  All  these  purposive  re- 
actions of  the  body  depend  upon  the  presence  in  the 
blood  of  a  shghtly  increased  amount  of  adrenalin. 
The  administration  of  adrenalin  to  animals  also 
causes  their  blood  to  clot  more  quickly,  erects  their 
hair,  and  dilates  their  pupils.  Adrenal  excess,  due 
to  hypertrophy  of  the  cortex,  causes  high  blood 
pressure,  and  in  w^omen  a  tendency  to  masculinity. 
Depletion  of  the  adrenal  reserves,  on  the  other  hand, 
leads  to  the  conditions  know^n  as  neurasthenia, 
nervous  breakdown,  chronic  fatigue,  and  shell  shock. 
If  differences  in  endocrine  activity  are  characteristic 
of  the  races  of  mankind,  then  such  differences  are 
inherited.  Are  smaller  glandular  differences  between 
the  individuals  of  the  same  race  inherited  ?  This 
thesis  is  supported  by  Berman  (i  921)  in  a  book  on  the 


SOCIAL  AND  WORLD  ASPECTS  219 

Glands    Regulating    Personality.     The    qualities    con- 
stituting personality  have  long  eluded  analysis.     In 
the    Middle   Ages   the   problem   was   viewed    as    one 
of   humours    in  the  blood,  giving   rise    to    a    bilious, 
lymphatic,    nervous,   or    sanguine    temperament.     If 
personalities    are    determined    by    the    quantities    of 
various     hormones    poured    into    the    blood    by    the 
endocrine    glands,    then    the   old   conventional    view 
was  not  so  very  far  wrong  after  all,  although,  of  course, 
the  views  of  the  Middle  Ages  had  no  such  definiteness 
It   is   not   improbable,   as   Berman   holds,   that   each 
individual   has   inherited    a    certain    constellation    of 
endocrine  activities,  but  it  seems  likely  that  he  has 
exaggerated  their  all-importance  in  the  determination 
of   the   personality.      He   recognises    three    types    of 
personality,    thyroid-centred,    pituitary-centred,   and 
adrenal-centred,  regarding  all  personalities  as  com- 
binations of  these.     Each  of  the  three  t^'pes,  he  says, 
is  "  stamped  with  a  significant  figure,  height,  skin, 
hair,   temperament,    ambition,   social   reactions,    and 
predisposition  to  certain  diseases."     Individual  facial 
types  are  also  regarded  as  the  expression  of  endocrine 
differences.    Whether  the  forehead  is  broad  or  narrow, 
the  distance  between  the  e3"es  great   or    small,   the 
character    of    the    eyebrows,    the    shape,    size,    and 
appearance  of  the  eyes,  the  mould  of  nose  and  jaws, 
and  peculiarities  of   the  teeth — all  are  regarded   as 
determined    by    hormone    differences.     Indeed,    the 
individual  is  looked  upon  as  a  complicated  pattern  of 
designs  traced  by  the  hormones.     Onl}'  after  a  further 
analysis  of  the  relation  of  hormones  to  the  hereditary 
determiners    which    produce   fixed    quantitative    dif- 
ferences   in    their    activities     can    it    be    determined 
whether  such  a  view  is  too  extreme.     It  has  to  be 
remembered,    in    any    case,    that    differences    in    the 
nervous  system  are  also  inherited. 

Shelley's  face  is  characterised  b}'  Berman  as  hypo- 


220  HEREDITY  AND  EUGENICS 

thyroid,  with  its  oval  shape,  dehcate  features,  wide, 
high  brow,  large,  proininent,  and  vivacious  eyes,  and 
sensitive  lips.  A  hyperpituitar}^  face,  on  the  other 
hand,  is  distinguished  by  its  low  and  narrow  shape, 
square  protruding  jaw,  high,  thin,  straight  nose, 
marked  cheek-bones  and  eyebrow^s ;  while  a  subpitui- 
tary  face  is  round  with  receding  chin,  fat  cheeks,  and 
broader  and  flatter  nose.  The  physiognomy  and 
character  of  various  men  are  also  analysed  in  terms 
of  internal  secretions.  Napoleon  and  Nietzsche  are 
regarded  as  pituitocentric,  Darwin  as  a  neurasthenic, 
pituitocentric  genius,  Caesar  as  a  pituitocentric 
epileptic  with  too  much  adrenal  and  post-pituitary^ 
secretion.  This  method  seems  at  present  something 
like  the  older  phrenology,  where  much  latitude  was 
left  to  the  imagination.  But  it  seems  clear  that 
various  differences  in  endocrine  activity  are  inherited, 
and  with  further  knowledge  this  may  form  a  satis- 
factory basis  for  the  analysis  of  personahties  and 
their  inheritance.  It  is  eas}-  to  understand  that  if 
a  personality  is  in  part  determined  by  the  relative 
activity  of  several  endocrine  glands,  these  being  in 
turn  determined  by  various  factors  or  genes  located 
in  different  chromosomes  of  the  germ  plasm,  then  the 
recombinations  of  such  factors  in  later  generations 
would  give  a  complicated  situation  very  difficult  to 
analyse,  but  one  in  which  various  elements  of 
personalit}^  might  still  be  said  to  be  inherited.  Even 
if  the  personality  depended  entirely  upon  shifting 
cross-currents  of  hormone  control,  it  would  be 
extremely  difficult  to  investigate  the  inheritance  of 
the  germinal  factors  w^hich,  in  turn,  determined  plus 
or  minus  variations  in  the  activities  of  the  various 
endocrine  glands,  because  each  gland  produces  many 
effects,  and  some  of  these  effects  overlap  or  reinforce 
each  other.  If  the  hormone  view  of  personality  has 
any    sound    basis,    then    each    personality,    both    in 


SOCIAL  AND  WORLD  ASPECTS  221 

physical  configuration  and  ni  mental  activities,  is 
a  palimpsest  of  cross-patterns  and  developmental 
currents  blended  into  a  unified  whole.  But  many 
elements  of  the  personality  must  also  be  determined 
by  mental  differences  based  on  inherited  differences 
in  the  nervous  system. 

The  Results  of  Crossing  between  Races. 

Eugenic  wTiters  differ,  according  to  their  social 
and  political  bias,  in  the  stress  they  lay  upon  a 
democratic  or  an  aristocratic  society  as  the  basis  f(jr 
eugenic  improvement.  This  difficult  question  we 
need  not  touch  upon  here,  except  to  point  out  that  the 
methods  of  eugenic  selection  may  differ  somewhat 
in  the  tw^o  cases.  The  stratification  of  society  in  older 
civilisations  appears  to  be  a  natural  process  {cf. 
Flinders-Petrie,  191 1),  which  has  often  been  at  first 
acquiesced  in  rather  than  promoted  by  human  arrange- 
ments, though  ultimately  petrified  and  perpetuated 
b}^  some  form  of  caste.  An  aristocratic  society  might 
be  supposed  to  be  composed  of  strains  which  wert- 
more  or  less  "  pure  lines  "  as  regards  their  distin- 
guishing characteristics,  but  this  is  seldom,  if  ever, 
the  case.  The  chief  reason,  of  course,  is  that  society 
is  so  largely  founded  upon  monetar}^  considerations, 
and  each  class  is  therefore  continually  receiving- 
recruits  from  other  classes.  In  a  population  of  real 
pure  lines,  such  as  wheat  or  garden  beans,  the  process 
of  selection  for  any  given  quality  is  simpler  than  in 
a  hybrid  population,  for  it  consists  merely  in  finding- 
one  or  a  few  individuals  with  the  desired  qualities, 
and  giving  them  the  opportunity  of  increased  pro- 
pagation. 

On  the  other  hand,  an  obvious  weakness  of  an 
aristocratic  society  from  the  point  of  view  of  eugenics 
and   heredity  is   the  fact  that  while  titles  arc  usually 


222  HEREDITY  AND  EUGENICS 

conferred  in  the  first  instance  as  a  recognition  of 
exceptional  ability  or  initiative,  ^xt  the  inheritance 
of  that  abilit}'  will  probabl}'  follow  different  rules  in 
different  cases,  and  eldest  sons  are  as  likely  as  not 
to  receive  other  qualities  from  their  father,  but  not 
his  abilit}'.  Ability,  like  genius,  is  probably  often 
due  to  a  fortunate  concatenation  of  favourable 
elements,  and  if  these  are  independently  inherited 
the  chances  of  their  reappearance  in  the  offspring  are 
small.  Nevertheless,  it  must  be  admitted  that  the 
exceptional  individual  has  a  much  better  chance  of 
transmitting  his  qualities,  or  some  of  them,  than  the 
average  individual  can  possibh^  have.  Yet  titles, 
no  doubt,  often  long  survive  any  expression  of 
exceptional  qualities  in  their  holders.  And  once  the 
quality  is  gone,  through  having  failed  to  be  inherited, 
cross-breeding  alone  can  bring  it  back.  Would  it  not 
seem,  then,  that  societ}'  founded  upon  ability  and 
quality,  and  not  upon  wealth,  in  which  there  was 
also  a  measure  of  latitude  in  intermarriage,  would 
be  in  consonance  with  the  eugenic  ideal  ? 

While,  therefore,  intermarriage  of  diverse  strains 
is  important,  both  from  the  point  of  view  mentioned 
above  and  on  account  of  the  increased  vigour  resulting 
from  a  heterozygous  condition,  yet  there  are  important 
limitations  to  the  width  of  the  crosses  which  are  desir- 
able. In  the  newer  countries,  such  as  North  and 
South  America  and  parts  of  Africa,  the  cross-bred 
races  which  have  sprung  up  through  miscegenation 
between  Europeans  and  more  backward  peoples  are 
at  a  disadvantage  from  almost  every  point  of  view. 
Physical  disharmonies  result,  such  as  the  fitting  of 
large  teeth  into  small  jaws;  or  as  Davenport  (igiyb) 
points  out,  large  men  with  small  internal  organs,  or 
inadequate  circulator}^  s^'stems,  or  other  disharmonies 
which  tax  the  adjustability  of  the  organism,  and  may 
lead  to  earl}-  death.     (But  see  p.  29.)     Segregation 


SOCIAL  AND  WORLD  ASPECTS  223 

of  characters  thus  results  in  a  motley  assortment  of 
types,  with  some  primitive  and  some  advanced 
mental,  moral,  or  physical  qualities  in  place  of  the 
original  more  or  less  blended  condition  in  the  first 
generation  of  the  cross.  It  is  questionable  even  if 
marriages  between  North  and  South  European  races 
are  always  wholly  desirable  in  their  results ;  although 
history  shows,  on  the  other  hand,  that  the  inter- 
mixture of  more  closely  related  races  is  beneficial 
as  supplying  increased  vigour  and  a  greater  range  of 
alternative  characters,  to  increase  the  potentialities 
of  the  population  or  for  selection  to  play  upon. 

Not  only  within  the  historical  period  (see,  for 
example,  Haddon,  191 9),  but  also  among  the  races 
of  Neolithic  and  Palaeolithic  man  there  is  evidence 
of  the  frequent  shifting  of  peoples  in  various  parts  of 
the  world.  Sometimes  the  defeated  race  was  driven 
out  or  exterminated,  but  ver}-  often  such  migrations 
resulted  in  the  fusion  of  two  races  into  a  new  unit 
ultimately  having  certain  uniform  and  distinctive 
features.  It  is  evident  that  h^'bridisation  has  been 
going  on  in  this  way  at  intervals  throughout  the 
histor}-  of  man.  It  does  not  follow,  as  some  writers 
assume,  that  crossing  is  the  cause  of  the  evolution, 
but  it  does  follow  that  the  great  majority  at  least  of 
modern  races  are  hybrid  in  origin,  although  they  may 
have  become  quite  uniform  through  isolation  and 
inbreeding.  The  fact  is  that  any  racial  unit  contains 
the  potentialities  of  innumerable  minor  races  if  these 
could  be  separated  out  and  inbred.  The  range  of 
migration  of  a  people  is  an  important  element  in 
determining  how  many  distinct  types  will  occupy  a 
given  area  of  territor}'.  When  the  Indian  tribes  of 
the  central  plains  of  North  America  took  to  a  nomadic 
life  after  the  introduction  of  the  horse,  many  of  the 
tribal  differences  between  them  quickly  disappeared. 
Differences    can    only    grow    up    in    a    condition    of 


224  HEREDITY  AND  EUGENICS 

isolation.  This  evolutionary  principle  of  isolation 
is  of  enormous  importance  and  has  usually  been 
overlooked  by  anthropologists. 

The  question  is  often  discussed  as  to  whether 
modern  man  is  a  single  species  or  more  than  one. 
The  fact  that  all  the  races  of  mankind  are  fertile  with 
each  other  is  no  longer  a  sufficient  reason  for  class- 
ing them  as  one  species.  The  present  generation  of 
naturalists  is  describing  innumerable  species  of  plants 
and  animals  as  distinct  species,  although  they  are 
perfecth^  fertile  with  each  other.  Sterility  as  a 
criterion  of  species  has  almost  completely  broken 
dow^n.  The  origin,  causes,  and  nature  of  inter- 
specific sterility  are  still  largely  obscure.  On  the  one 
hand,  species  of  Drosophila,  so  closely  similar  that 
they  are  scarcely  distinguishable  even  by  experts, 
may  show  complete  sterility  with  each  other  or,  at 
least,  provide  onl}'  sterile  hybrids  ;*  while,  on  the  other 
hand,  all  the  species  of  cattle  {Bovidce)  are  inter- 
fertile,  although  man}^  of  them  show  striking 
differences.  In  mankind  the  differences  between  the 
five  great  colour  varieties  are  not  merely  in  the  skin 
colour,  but  also  in  such  points  as  stature,  hair  colour 
and  shape,  cranial  conformation,  facial  peculiarities, 
skin  secretions,  and  intelligence.  These  differences 
are  quite  as  distinctive  and  varied  as  those  betw^een 
many  described  species  of  higher  animals.  Such 
differences  could  only  have  grown  up  during  long 
periods  of  isolation,  and  can  only  be  maintained  by 
isolation  or  an  absence  of  crossing.  The  five  colour 
types  of  mankind  also  occupied,  until  modern  trans- 
portation began,   more   or    less   marked^  separated 

*  Even  more  extreme  are  the  various  cases  of  self-sterility  in 
plants,  in  which  many  of  the  individuals  are  sterile  with  their 
own  pollen.  In  such  cases  as  Primula,  crosses  between  individuals 
of  the  same  species  but  having  different  types  of  flower  are  more 
fertile  than  self-fertilised  plants. 


SOCIAL  AND  WORLD  ASPECTS  225 

areas  of  the  earth's  surface,  althoui^h  where  the  yellow 
and  brown  races,  for  example,  are  in  contact  in  south- 
eastern x\sia  a  gradual  transition  occurs  between  them. 
Where  evolution  has  been  going  on  independently  in 
these  races  for  such  long  periods,  and  some  races  have 
progressed  far  beyond  others,  both  mentall}'  and 
culturally,  it  is  foll}^  to  suppose  that  crosses  between 
a  progressive  and  a  primitive  race  can  lead  to  a  desir- 
able result  from  the  point  of  view  of  the  advanced 
race,  or  even  of  the  primitive  race.  Many  native 
African  and  other  tribes  are  in  the  Stone  Age,  so  far 
as  their  culture  is  concerned,  and  it  cannot  be  ex- 
pected that  their  mentality  has  advanced  beyond 
that  period.  The  mental  status  of  the  average 
Palaeolithic  man  is  difficult  to  determine.  Although 
the  mental  capacity  of  modern  man  has  not  increased 
during  the  historical  period,  yet  it  is  necessary  to 
suppose  that  the  development  of  the  human  mind 
has  consisted  in  something  more  than  the  mere 
accumulation  of  tradition.  In  other  words,  there 
has  been  a  real  evolution  in  which  the  mind  has  been 
one  of  the  reacting  elements.  The  mental  level  of 
the  average  Palaeolithic  man  can  hardly  have  been 
higher  than  that  of  our  modern  feeble-minded.  The 
Australian  black-fellow  appears  to  be  an  earh'  Pakeo- 
lithic  survival,  resembling  Mousterian  man,  and 
wholly  incapable  of  coping  with  the  white  man's 
civilisation.  It  is  clear  that  other  races  represent 
different  stages  of  mental  development. 

This,  of  course,  is  often  disputed,  and  it  is  frequently 
held  that  Palaeolithic  man  was  potentially  the  mental 
equal  of  modern  civilised  man.  This  depends  on  the 
sense  in  which  the  term  "  potential  "  is  used.  The 
important  point  is  that  primitive  races  are  largely 
incapable  of  taking  hold  of  the  white  man's  civilisa- 
tion and  profiting  by  it,  or  adapting  it  to  their  own 
use,  except  in  a  primitive  way.     No  doubt,  as  Carr- 

13 


226  HEREDITY  AND  EUGENICS 

Saunders  (1922)  holds,  man's  mental  evolution  has 
consisted  largely  in  the  handing  down  of  accumulated 
tradition,  but  there  must  also  have  been  a  reaction 
of  man's  mind' — that  is,  a  mental  evolution — in  order 
to  make  the  continued  accumulation  and  advance  of 
tradition  possible.  That  such  a  mental  evolution  has 
accompanied  the  accumulation  of  tradition  is  evident 
from  the  recent  history  of  the  Japanese.  They  were 
able  in  one  generation  to  absorb  a  great  part  of 
Western  science  and  begin  making  independent 
contributions  to  that  science.  This  remarkable 
phenomenon,  resulting  from  contact  with  Western 
civilisation,  has  not  been  approached  by  any  truly 
primitive  people,  which  shows  that  primitive  peoples 
w^ould  require  a  long  period  of  mental  evolution  before 
they  were  capable  of  grasping  or  profiting  by  the 
views  of  nature  held  in  the  civilised  world. 

As  we  have  already  pointed  out,  crossing  between 
more  or  less  related  races  or  tribes  of  mankind  has 
been  going  on  at  intervals  throughout  the  whole  of 
historical  and  prehistoric  time.  Nevertheless,  at  any 
given  period  it  has  usually  been  confined  to  definite 
areas  of  contact  between  tribes,  and  has  been  very 
limited  in  its  scope,  except  at  times  of  migrating  or 
shifting  populations.  Primitive  man,  in  particular, 
was  far  less  of  a  roving  animal  than  is  commonly 
supposed.  This  is  shown  by  the  great  number  of 
local  native  tribes  which  existed  among  the  Indians 
of  North  and  South  America  at  the  time  of  their  first 
contact  with  European  civilisation.  Such  differentia- 
tion, like  that  of  any  other  species,  could  only  have 
occurred  under  conditions  of  relative  isolation  and 
segregation — i.e.,  absence  or  infrequency  of  inter- 
marriage. Carr-Saunders  (1922)  has  pointed  out  that 
as  soon  as  early  man  began  to  have  am^  social  organ- 
isation at  all,  probabty  even  as  earty  as  the  Upper 
Palaeolithic,   families   and  groups   began  to   develop 


SOCIAL  AND  WORLD  ASPECTS  227 

hunting  and  fishing  and  general  food-getting  rights 
over  fixed  hniited  areas.  Among  the  primitive  races 
of  modern  times  these  conditions  continue.  For 
instance,  in  parts  of  former  German  South-West 
Africa,  where  the  chief  Hottentot  food-plant  on  parts 
of  the  coast  is  a  gourd,  Acanthosicyos  horrida,  growing 
on  the  sand-dunes,  individual  families  and  groups 
have  vested  rights  over  the  fruits  of  this  plant  in 
local  areas,  and  it  annually  saves  their  lives  and 
serves  as  a  source  of  both  food  and  water  until  other 
food  is  obtainable.  Native  groups  are,  then,  not  free 
to  wander  at  will  wherever  fancy  dictates,  but  each 
party  is  confined  to  a  limited  area,  whose  boundaries 
are  definitely  known  to  them.  This  fact,  that  each 
group  is  definitely  tied  to  a  local  area  by  recognised 
custom  and  is  often  at  war  with  its  neighbours,  adds 
greatly  to  the  stabilit}^  of  any  savage  population, 
and  probably  lessens  the  amount  of  exogamy  between 
unrelated  families.  These  are  the  conditions  under 
which  local  tribes  and  differentiated  groups  might 
be  expected  to  grow  up.  Such  a  process  of  differentia- 
tion is,  however,  ver}^  slow,  and  the  spread  of  culture 
from  group  to  group  will  also  tend  to  the  maintenance 
of  uniformit}'.  Nevertheless,  cultural  differences, 
owing  to  local  environmental  conditions,  will  arise 
long  before  structural  differences  appear,  and  in  the 
tribes  of  North  American  Indians  such  structural 
differences  seem  to  have  been  ver}^  few.  Languages, 
on  the  other  hand,  were  many  and  often  widely 
different  (though  showing  evidences  of  a  common 
origin),  w^hich  implied  a  long  period  of  cultural 
isolation. 

The  results  of  crosses  between  such  related  tribes 
are  relativel}'  insignificant,  the  differences  involved 
being  less  than  those  between  the  peoples  of  European 
nations.  Crosses  between  equally  primitive  or  equally 
advanced  peoples  of  similar  culture  involve  no  very 


228  HEREDITY  AND  EUGENICS 

serious  problem.  Inter-crossing  between  races  more 
remotely  related,  especiall}'  when  one  is  primitive 
and  the  other  advanced,  immediately  involve  prob- 
lems of  the  utmost  difficulty — problems  which  may 
be  said  to  have  arisen  seriously  onl}^  in  modern  times. 
These  problems  require  study  in  three  separate 
aspects  :  (i)  In  crosses  between  primitive  races;  (2)  in 
crosses  between  a  primitive  and  an  advanced  race ; 
(3)  in  crosses  between  advanced  races.  In  each  case 
the  results  of  the  particular  cross  must  be  taken  into 
account.  For  instance,  crosses  between  Europeans 
and  Bantu  peoples  might  be  undesirable  from  am^ 
point  of  view,  while  marriages  between  Europeans 
and  Polynesians  might  conceivably-  produce  a  more 
felicitous  result. 

Wallace  (Alalay  Archipelago,  p.  335)  states  that 
*'  Everywhere  in  the  East  where  the  Portuguese 
have  mixed  with  the  native  races  the}-  have  become 
darker  in  colour  than  either  of  the  parent  stocks"; 
but  that  "  the  reverse  is  the  case  in  South  America, 
where  the  mixture  of  the  Portuguese  or  Brazilian 
with  the  Indian  produces  the  '  Mameluco,'  who  is  not 
unfrequently  lighter  than  either  parent,  and  always 
lighter  than  the  Indian."  Such  results  might  be 
expected  if  skin  colour  were  controlled  by  differences 
in  the  activity  of  various  endocrine  glands. 

Very  few  serious  studies  of  the  results  of  racial 
crossing  have  been  made,  and  probably  no  field  of 
anthropology  could  be  more  profitably  explored  at  the 
present  time.  The  Pitcairn  and  Norfolk  Islanders 
w-ould  form  a  valuable  basis  for  such  a  study.  They 
are  descended  from  ten  English  sailors,  who  mutinied 
in  a  voyage  to  Tahiti  in  1788,  and  with  eighteen 
native  Polynesians  (six  men  and  twelve  women) 
formed  a  colony  on  the  little  island  of  Pitcairn.  In 
1856  the  resulting  population  of  200  overflowed  to 
Norfolk  Island,  and  the  descendants  of  this  crossed 


SOCIAL  AND  WORLD  ASPECTS  229 

race  on  the  two  islands  now  number  about  a  thousand. 
They  should  form  excellent  material  for  an  anthro- 
pometric study  of  a  population  descended  through 
several  generations  from  original  crosses  between 
English  and  Polynesians. 

The  most  ambitious  of  such  studies  which  has  yet 
been  made  is  probably  that  of  Fischer  (191 3)  on  the 
Reheboth  hybrid  people  inhabiting  a  portion  of  the 
area  which  was  formerly  German  South- West  Africa. 
These  people  were  derived  from  crosses  between 
Hottentot  women  and  Boer  men,  which  began  over 
a  century  ago.  They  now  number,  perhaps,  3,000. 
In  a  general  anthropological  and  ethnographical  study 
of  these  people,  Fischer  concludes  that  they  are  a 
well  characterised  but  very  variable  group.  The 
characters  of  the  parent  races  are  combined  in  the 
greatest  variety  of  ways,  showing  continued  segrega- 
tion, and  not  a  permanent  blend.  The  first  crosses  are, 
in  general,  intermediate,  and  when  crossed  back  with 
either  race,  they  resemble  more  the  race  with  which 
they  were  recrossed.  They  are  said  to  be  sound, 
strong,  and  ver}^  fertile,  having  an  average  of  7-4 
children  per  famil}^  The  inheritance  of  individual 
characters,  such  as  hair  form  and  colour,  eye  colour, 
skin  colour,  shape  of  nose,  nasal  index,  form  of  eyelid, 
breadth  of  forehead,  etc.,  was  studied  and  found  to 
show  alternative  inheritance;  but  the  observations, 
while  valuable,  are  scarcel}'  sufficiently  detailed  to 
furnish  critical  evidence  on  all  these  points.  Never- 
theless, a  body  of  valuable  data  of  inheritance  is 
brought  together.  An  important  conclusion  reached 
is  that  the  size  of  body  and  length  of  face  is  greater 
than  in  either  parent  race,  while  the  fertility  is  found 
to  be  undiminished  and  the  sex  ratio  unaltered. 

The  latter  conclusion  is,  however,  not  in  harmony 
with  the  statistical  data  on  the  sex  ratio  in  hybrids 
obtained  by  other  investigations.      Thus,  Pearl  and 


230  HEREDITY  AND  EUGENICS 

Pearl  (1908)  examined  the  vital  statistics  of  the  city 
of  Buenos  Ayres,  where  Italian,  Spanish,  and  Argentine 
crosses  take  place,  the  last  being  itself  a  mixed  race. 
The  data  extended  over  a  period  of  ten  years,  and 
made  possible  the  comparison  of  the  sex  ratio  in  pure 
matin2:s  with  that  in  crosses.  In  the  former  case  the 
ratio  was  102-21  :  100,  in  the  latter  105-99:  100,  hence 
a  greater  excess  of  male  offspring  from  cross-matings. 
Little  (19 1 9)  has  made  a  similar  study  of  the  sex 
ratios  from  the  records  of  a  lying-in  hospital  in  New^ 
York.  These  records,  unlike  the  previous  ones,  in- 
cluded still-births,  and  the  types  of  matings  included 
(i)  those  within  each  of  the  following  nationalities: 
English,  Irish,  Scotch,  Italian,  Russian,  Greek, 
Austrian,  and  German;  (2)  all  possible  first  genera- 
tion matings  between  members  of  these  nationalities. 
The  results  gave  a  sex  ratio  of  106-27  for  the  pure 
stocks,  and  121-56  for  the  crosses.  This  indicates 
an  even  more  marked  increase  of  male  births  in  the 
hybrid  stocks  than  the  Argentine  statistics.  Separate 
examination  of  the  data  for  still-births  indicated 
that  they  were  more  frequent  in  the  pure  races  than 
in  the  crosses.  These  results  indicate  that  in  crosses 
betw^een  European  races  there  is  a  higher  ratio  of 
male  births  and  a  lower  frequency  of  still-births,  at 
least  in  the  first  generation.  The  latter  is  probably 
a  result  of  hybrid  vigour.  That  crossing  a  species 
may  alter  the  sex  ratio  of  the  offspring  in  very 
marked  degree  has  also  been  shown  in  the  case  of 
pigeons  and  other  animals. 

Returning  to  the  subject  of  racial  crossing,  re- 
ference may  be  made  to  a  short  study  of  racial 
mixture  in  Hawaii  (MacCaughey,  191 9).  In  these 
islands  intermarriages  of  Portuguese,  Spanish, 
Haw-aiian,  Chinese,  Japanese,  Americans,  English, 
and  other  Europeans  are  taking  place.  The  popula- 
tion  containing   this   remarkable   diversity   of  races 


SOCIAL  AND  WORLD  ASPECTS  231 

numbers  about  246,500,  the  Japanese  predominating 
in  numbers.  From  a  decade  of  observation  of  this 
microcosmic  mehing-pot,  the  conclusion  is  reached 
that  such  racial  intermingling  is  usually  undesirable 
in  its  results.  Most  of  the  Caucasian*-Hawaiians 
seem  to  blend  the  least  desirable  traits  of  both 
parents,  and  intermarriages  of  North  European  and 
American  stocks  with  dark-skinned  races  are  con- 
sidered biologically  wasteful. 

Similarly  Lundborg  (1920),  from  a  study  of  Swedish 
conditions,  concludes  that  the  crossing  of  races 
degenerates  the  constitution  and  increases  degrada- 
tion. He  finds  such  crossing  much  more  common  in 
the  poorer  and  lower  classes,  while  the  middle  classes 
are  more  homogeneous.  In  the  lower  classes  are 
more  frequently  found  individuals  with  other  race 
characters — e.g.,  darker  hair  and  eyes.  Mjoen  (1922) 
has  examined  the  results  of  crosses  in  Norway  between 
the  Nordics  and  the  Mongoloid  Laplanders .  He  found 
the  first  generation  to  be  taller  and  heavier  than  the 
tall  Nordic  parent  (owing  to  heterosis),  but  that  this 
increase  in  size  is  lost  in  later  generations.  Also, 
frequently  in  crosses  between  Lapps  and  Norwegians, 
especially  when  Alpine  blood  was  also  present,  a 
mentally  unstable  type  is  produced,  the  lack  of 
balance  being  shown  by  stealing,  lying,  and  drinking. 
A  similar  unbalanced  type  frequently  arises  from 
crosses  between  American  Indians  and  French  or 
English.  The  writer  concludes  that  as  regards  these 
matings,  the  pure  races  have  the  advantage  in  every 
way.  For  example,  the  incidence  of  tuberculosis  is 
the  lowest  (i-i  to  1-5)  where  the  Nordic  race  is 
comparatively  pure,  and  highest  (3-6  to  4)  in  the 
region  where  there  is  the  largest  race  mixture. 

As  regards  world  eugenics,  then,  it   would   appear 

*  This  loosely  used  term  is  meant  to  include  Europeans  and 
Americans  belonging  to  the  "  white  "  race. 


232  HEREDITY  AND  EUGENICS 

that  intermixture  of  unrelated  races  is  from  ever}* 
point  of  view  undesirable,  at  least  as  regards  race 
combinations  involving  one  primitive  and  one  ad- 
vanced race.  It  is  possible  that  crosses  between  an 
advanced  and  a  native  race  mav  be  advantageous 
as  leading  to  progress  in  certain  tropical  regions 
where  the  white  man  cannot  survive,  although  the 
results  of  such  interbreeding  in  various  tropical 
countries  do  not  lead  to  a  very  hopeful  outlook.  But 
the  melting-pot  conception  is  being  discredited  b}' 
eugenic  writers  in  the  United  States,  where  inter- 
crossing has  been  taking  place  on  a  great  scale.  It 
ma}'-  now  be  recognised  that  while  interbreeding  of 
related  races  or  strains  gives  increased  vigour,  at  least 
in  the  F^  generation,  crosses  on  a  large  scale  between 
more  distant  races  which  have  for  ages  been  separately 
evolving  create  unnecessary  problems,  and  are,  for 
the  most  part,  wholly  undesirable  in  their  results. 
The  more  advanced  race  is  diluted  and  degraded  by 
such  intermixture,  and  primitive  mental  and  moral 
characters  are  placed  on  a  level  with  the  more  highly 
evolved.  Moreover,  Goddard  (191 7),  in  discussing 
mental  tests  for  immigrants  into  the  United  States, 
states  that  the  average  steerage  passenger  is  of  low- 
grade  intelligence,  perhaps  even  feeble-minded.  He 
examined  six  small  groups  arriving  at  Ellis  Island, 
by  means  of  the  Binet  scale  tests,  and  found  that 
only  2  in  148  scored  as  high  as  twelve  years,  which  is 
regarded  as  the  line  between  feeble-minded  and 
normal.  These  people  included  Italians,  Russians, 
Jews,  and  Hungarians.  His  conclusion  is  that  there 
is  a  high  percentage  of  feeble-minded  among  the 
present  immigrants. 

Even  after  a  thousand  years  of  intermarriage, 
separate  racial  traits  may  still  be  traceable  in  the 
modern  Englishman.  The  blend  is  only  a  blend 
when     considered     en     masse.      Alternative     inheri- 


SOCIAL  AND  WORLD  ASPECTS  233 

tance,  and  more  or  less  complete  segregation,  still 
appear  as  regards  single  characters.  The  various 
types  of  modern  Italian,  viewed  in  the  light  of  their 
history,  appear  to  show  the  same  thing.  Although 
innumerable  racial  unions  have  taken  place  in  the 
histor}^  of  mankind,  yet  the  elements  distinguish- 
ing the  original  races  appear,  for  the  most  part, 
to  retain  their  separate  identity  and  independent 
transmission  in  inheritance.  The  resulting  race  con- 
sidered as  a  population  will  be  a  blend  of  the  original 
races,  yet,  for  a  long  period  at  least,  the  elemental 
differences  continue  to  be  separately  inherited. 
Whether,  ultimatel}^  a  real  blend  occurs  is  uncertain, 
but  if  it  ever  does  this  mav  be  onlv  after  a  thousand 
years  or  so  of  interbreeding  within  the  hybrid  race. 
In  any  case  the  racial  elements  of  the  more  primitive 
stock  will  dilute  and  weaken  the  better  elements  of 
the  more  progressive  stock,  with  a  retarding  or 
degrading  effect  on  the  progressive  stock  as  a  whole. 
It  is,  therefore,  clear  that  miscegenation  between,  for 
example,  the  white  races  and  African  races — which  for 
ages  have  been  undergoing  separate  evolution  which 
must  have  been  at  ver}'  different  rates,  assuming  that 
both  are  descendants  from  the  same  original  stock — 
is  wholly  undesirable  from  a  eugenic  or  any  other 
reasonable  point  of  view. 

Yet  it  cannot  be  gainsaid  that  the  negro  in  the 
United  States,  through  interbreeding  chiefly  with  the 
lowest  strata  of  whites,  is  already  producing  a  visible 
effect  on  the  colour  and  features,  and  surely  also  on 
the  mentalit}'  of  those  elements.  Unless  this  process 
is  checked,  the  ultimate  result  would  appear  inevitably 
to  be  a  gradual  incorporation  of  these  more  primitive 
elements  in  the  whole  population.  The  brain  of  the 
average  negro  weighs  3  or  4  ounces  less  than  that  of 
the  average  white  man,  but  this  in  itself  does  not 
necessarily  prove  a  lower  intelligence,  because  it  is 


234  HEREDITY  AND  EUGENICS 

well  known  that  men  of  exceptional  abilit}^  frequentl}^ 
have  small  brains.  Ferguson  (1921),  in  a  sane  dis- 
cussion of  the  mental  status  of  the  American  negro, 
concludes  that  psychological  study  of  the  negro  in- 
dicates that  he  will  never  be  the  mental  equal  of  the 
white  man.  Comparison  of  school  children  in  the 
elementar}^  grades  shows  that  onl}'  20  or  25  per  cent, 
of  negro  children  equal  or  exceed  the  average  score 
of  white  children.  But  the  term  "  negro  "  in  these 
and  other  American  statistics  includes  every  grade  of 
mulatto,  and  the  latter  ma}^,  of  course,  inherit  the 
ability  of  their  white  ancestor.  If  only  pure  negroes 
were  considered,  their  average  mental  ability  would 
probably  be  much  lower.  The  United  States  census 
of  1 910  show^ed  that  mulattoes  constituted  ap- 
proximately one-fifth  of  the  coloured  population, 
a  fraction  which  continues  to  increase  and  is  now 
probably  one -fourth.  Mental  tests  of  coloured 
children  in  schools  show  that,  on  the  average,  lighter 
skin  goes  with  higher  intelligence. 

The  American  army  intelligence  tests  showed  a  still 
more  marked  difference  between  whites  and  blacks. 
Only  one-third  of  the  negroes  were  sufficiently  literate 
to  read  a  newspaper  or  write  a  letter,  while  three- 
fourths  of  the  whites  passed  this  test.  The  result 
was  probably  partly  due  to  a  difference  in  educa- 
tional opportunities,  but  the  Binet  tests,  which 
measure  ability  apart  from  education,  showed  that 
only  20  to  25  per  cent,  of  the  "  negro  "  recruits 
equalled  or  exceeded  the  average  white  recruit. 
Moreover,  the  percentage  of  mulattoes  among  the 
literates  was  about  twice  as  great  as  among  the 
illiterates,  and  when  the  illiterates  were  removed 
from  a  "  negro  "  company  its  complexion  was  thereby 
notably  lightened.  While  the  negro's  mental  status 
is  thus  undoubtedly  more  primitive  than  that  of  the 
white  man,  yet  there  is  apparently  no  evidence  for  the 


SOCIAL  AND  WORLD  ASPECTS  235 

doctrine  that  his  mental  growth  ceases  at  adolescence. 
Many  writers  regard  the  negro  as  a  case,  not  of 
arrested  mental  development  which  might  be  over- 
come by  educational  effort  (although  the  utmost  effort 
in  education  does  not  prevent  the  arrest  in  mental 
development  of  the  feebleminded),  but  of  a  primitive 
mentality  with  less  control  of  the  impulses  and 
emotions  and  less  ability  to  deal  with  the  abstract 
or  symbolic.  The  wisdom  of  Booker  T.  Washington's 
programme  of  manual  education  for  the  negro  as 
most  appropriate  to  his  mental  status  is  clearly  shown. 
As  far  as  the  muscular  and  nervous  systems  and  the 
sense  organs  are  concerned,  there  is  apparent^  no 
great  difference  between  negroes  and  whites,  but  that 
physical  differences  exist  is  shown  by  the  data  in  the 
following  paragraph. 

Love  and  Davenport  (191 9),  from  an  analysis  of  the 
sick  reports  of  American  troops  in  camp  in  the 
United  States  during  the  war,  find  some  notable 
differences  between  white  and  coloured  troops.  That 
negroes  are  relatively  lacking  in  resistance  to  tuber- 
culosis and  pneumonia  is  shown  by  the  fact  that  the 
rate  for  tuberculosis  was  over  twice  as  high  among 
coloured  troops,  while  for  pneumonia  it  was  two  or 
three  times  as  high.  The  rate  for  venereal  disease 
is  three  or  four  times  higher  in  coloured  troops, 
epilepsy,  hysteria,  neuralgia,  and  haemorrhoids  are 
about  twice  as  frequent,  addiction  to  drugs  is  more 
common,  while  skin  diseases  are  less  common  than  in 
white  troops.  That  not  only  the  skin  but  also  the 
lining  of  the  mouth  and  naso-pharynx  is  more  re- 
sistant,* is  shown  by  the  lesser  frequency  of  diphtheria, 
scarlet  fever,  German  measles,  and  influenza.  The 
nervous  system  of  the  negroes  also  showed  less 
liability    to    neurasthenia    and    alcoholism,    eye    and 

*  It  seems  more  probable  that  the  greater  incidence  of  respira- 
tory diseases  among  negroes  is  due  to  their  wide  flaring  nostrils. 


236  HEREDITY  AND  EUGENICS 

ear  defects  were  about  half  as  common  as  in  whites, 
and  there  were  fewer  cases  of  metabohc  disturbance, 
such  as  diabetes  and  urinary  calcuh.  It  thus  appears 
that  the  negro  is  a  better  animal  as  far  as  e3'es  and 
ears  are  concerned,  has  a  more  protective  skin  and 
a  less  easily  deranged  metabolism,  but  is  less  resistant 
to  diseases  of  the  lungs  and  pleura  and  to  some  of  the 
general  diseases. 

Discussing  the  results  of  the  mingling  of  races  in 
the  United  States  through  immigration,  Davenport 
(191  7)  states  that  nearly  two-thirds  of  the  9,000,000 
population  of  New  York  State  are  foreign  born,  or  of 
foreign  or  mixed  parentage.  Nearly  all  the  European 
countries  are  represented,  most  of  them  b}'  many 
thousands,  and  intermingling  of  races  in  the  country 
at  large  is  taking  place  on  a  scale  never  before  ap- 
proached in  the  histor}-  of  man.  The  irregular 
dentition  which  makes  orthodontia  a  recognised 
branch  of  dentistry  may  be  a  result  of  disharmonies 
between  teeth  and  jaws  in  the  various  crossed  races, 
a  condition  in  marked  contrast  with  the  regular 
dentition  of  native  races,  though  such  conditions  may 
also  arise  from  malnutrition.  Davenport  concludes 
that  miscegenation  commonly  results  in  disharmony 
of  physical,  mental,  and  temperamental  qualities, 
often  leading  to  disharmon}'  with  the  environment 
and  consequent  unhappiness.  A  hybridised  people 
will  tend  to  be  restless,  dissatisfied,  and  ineffective; 
the  high  death-rate  in  middle  life  ma}'^  be  due  to  bodil}' 
maladjustments,  and  much  of  the  crime  and  insanity 
to  the  inheritance  of  badh'  adjusted  mental  and 
temperamental  differences.  It  is  probable  that  in 
such  a  very  heterogeneous  mixture,  in  which  there 
has  been,  until  recently,  little  selection  or  often  even 
negative  selection  of  the  original  immigrant  elements, 
the  disadvantages  and  disharmonies  more  than  offset 
any  advantages  that  may  accrue  from  crossing.     To 


SOCIAL  AND  WORLD  ASPECTS  237 

look  for  a  higher  racial  type  from  the  indiscriminate 
blending  of  such  elements  appears  to  be  the  height 
of  folly. 

All  general  problems  of  race  and  movements  of 
population  are  closely  connected  with  questions  of 
birth-  and  death-rates.  In  an  able  analysis  of  the 
causes  of  death  in  man  from  an  evolutionary  and 
embryological  point  of  view,  Pearl  (1920)  has  shown, 
from  statistics  of  the  United  States,  England,  and 
South  Brazil,  that  man's  greatest  enemy  is  his  own 
endoderm.  In  the  two  former  countries  about 
57  per  cent,  of  all  deaths  which  are  biologically 
classifiable  result  from  breakdown  and  failure  to 
function  of  organs  derived  from  the  endoderm  in  their 
embryological  development.  Only  8  to  13  per  cent, 
of  deaths  result  from  breakdown  of  ectodermal 
organs,  the  remaining  30  to  35  per  cent,  being  ascribed 
to  organs  of  mesodermal  origin.  The  endoderm  has 
been  least  differentiated  in  evolution,  and  hence  is 
least  adapted  to  resist  the  vicissitudes  of  environment. 
Sanitary  and  public  health  measures  are  largely 
directed  to  softening  the  asperities  of  the  environment, 
so  that  the  relatively  inefticient  and  primitive  endo- 
derm can  cope  with  it.  Organologically  considered, 
the  respiratory  and  alimentary  systems  are  most 
largely  responsible  for  human  deaths.  Then  follow 
in  order  the  circulatorv  and  nervous  svstems,  the 
kidneys,  sex  organs,  skeletal  and  muscular  S3'stem, 
the  skin,  and  finalty  the  endocrinal  system  or  glands 
of  internal  secretion.  Differences  in  the  efficiency, 
structure,  and  functioning  or  tendency  to  disease  in 
all  of  these  groups  of  organs  no  doubt  exist  and  are 
inherited.  In  this  way  the  factor  of  heredity  directly 
affects  the  death-rate  in  families,  and  is  often  an 
important  element  in  determining  the  age  at  which 
death  will  take  place. 

It  is  now  well  known  from  the  statistical  records  of 


238  HEREDITY  AND  EUGENICS 

civilised  countries  that  birth-rates  and  death-rates 
usually  rise  and  fall  together.  A  very  good  discussion 
of  the  subject  is  by  Dean  Inge  ( 1 9 1 9) .  Notwithstand- 
ing the  numerous  factors  which  have  been  ascribed 
as  causes  of  the  waxing  and  weaning  of  birth-rates, 
populations,  and  civilisations,  we  are  still  largely 
in  the  dark  as  to  the  fundamental  biological  signi- 
ficance of  these  fluctuations.  Did  the  ancient  civilisa- 
tions fail  to  maintain  themselves  on  account  of 
climatic  changes,  soil  sterility,  malaria,  infanticide, 
losses  in  war,  inbreeding,  natural  sterility,  or  racial 
ennui  and  hopelessness  of  outlook  ?  All  of  these 
causes  may  have  been  operative  in  particular  cases, 
but  none  of  them  appear  to  be  adequate  to  account 
for  the  submergence  of,  for  example,  the  classic 
civilisations  of  antiquity.  We  see  the  sweep  of 
biological  wave  on  wave  of  population,  but  the 
nature  of  the  operative  forces  which  produce  these 
tides  is  too  complex  for  analysis  with  our  present 
knowledge. 

A  recent  wTiter  (Nilsson,  1921)  discusses  the  down- 
fall of  Greece  and  Rome  from  a  racial  and  biological 
point  of  view.  He  points  out  that  both  countries 
apparently  took  their  origin  b}^  the  establishment  of 
races  by  isolation  and  inbreeding  after  a  mixture  or 
invasion  of  races  had  taken  place.  There  was  a 
great  diversity  of  races  in  the  Roman  Empire,  and 
Roman  rule  tended  to  mix  them  up.  Previously 
isolation  and  inbreeding  had  kept  them  relatively 
fixed  and  developed  them  as  relatively  pure  races. 
Under  the  shelter  of  Roman  peace  and  Roman 
administration  they  mingled,  and  the  result  was 
unlimited  hybridising  of  types,  destroying  the  many 
fixed  types  which  had  existed,  and  giving  rise  to 
instability  of  disposition  and  of  culture.  This  blend- 
ing of  man}^  races  is  regarded  as  the  most  destructive 
agency  in  the  downfall  of  Rome.     This  would  furnish 


SOCIAL  AND  WORLD  ASPECTS  239 

an  unhapp}^  outlook  for  the  results  of  the  hetero- 
geneous intermixture  which  is  going  on  in  America 
on  a  scale  never  before  equalled.  Yet  we  can  scarcely 
believe  this  is  the  whole  story.  German  and  Gallic 
tribes  shifted  and  invaded  their  neighbours'  territories 
in  great  numbers  even  before  the  advent  of  Caesar. 
The  immediate  cause  of  some  at  least  of  these  move- 
ments was  a  flood  or  unfavourable  harvest  season, 
which  destroyed  their  narrow  margin  of  food  reserves 
and  made  it  necessary  for  large  numbers  to  seek  their 
subsistence  in  more  hospitable  conditions.  This 
appears  to  have  been  particularly  true  of  some  of  the 
early  Scandinavian  tribes.  An  increasing  population 
in  relation  to  local  climatic  conditions  and  food- 
supply  must  then  often  have  been  the  impelhng 
power.  Nevertheless,  relative  stability  of  tribal 
relations  was  maintained,  and  indiscriminate  mingling 
of  unrelated  races  only  began  under  Roman  rule. 

It  is  also  arguable  that  all  the  historic  civilisations 
have  been  correlated  with  the  presence  of  a  race  of 
superior  courage  and  initiative  dominating  the 
activities  of  an  inferior  race.  Their  civilisation  died 
out  when  the  ruling  race  failed  to  maintain  its  numbers, 
either  through  miscegenation  or  from  a  variety  of 
other  causes. 

Since  about  1876  the  birth-rate  in  various 
European  countries  has  steadily  declined,  falling 
from  36  per  1,000  in  England  and  Wales  to  about 
24  before  the  war.  Similarly  in  Germany  the  rate 
fell,  with  fluctuations,  from  nearly  41  in  1875  to  27-5 
in  191 3.  But  the  death-rate  dropped  concurrently 
in  England  and  Wales  from  237  in  1 864  to  the  pre-war 
figure  of  14,  and  a  similar  decline  occurred  in  Germany. 
After  many  w^ars  a  rise  in  the  birth-rate  soon  restores 
the  population.  Statistics  even  show  a  rise  in  the 
frequency  of  male  births  during  and  after  a  war. 
Although  it  is  difficult  to  understand  how  war  con- 


240  HEREDITY  AND  EUGENICS 

ditions  can  affect  this  ratio,  3^et  it  undoubtedly  appears 
to  be  the  case  that  in  some  wa}^  the  ratio  of  male  to 
female  births  is  increased,  so  closely  is  the  biological 
status  of  the  race  amenable  to  economic  conditions 
like  war  or  an  epidemic.  Emigration  also  leaves  a 
vacant  space  which  is  soon  filled  up  by  an  increased 
birth-rate,  but  as  Carr-Saunders  points  out,  the 
importance  of  emigration  in  this  respect  has  been 
greatly  overrated. 

The  nineteenth  century  was  a  period  of  rapid 
increase  in  population,  both  in  Europe  and  America, 
but  the  birth-rate  in  Europe  and  in  the  Anglo-Saxon 
population  of  America  has  been  falling  throughout 
the  last  quarter  of  that  century  and  the  subsequent 
two  decades,  though  there  may  be  a  temporary  rise 
following  the  war.  Of  course,  a  permanent  fall  in 
the  birth-rate  must  ultimately  take  place  when  the 
relatively  empty  countries  available  to  the  white  race 
have  been  filled  up.  The  serious  feature  of  the 
declining  birth-rate  is  its  differential  character,  for 
birth  control,  as  practised,  leads  to  a  condition  in 
which  we  are  breeding  most  largel}^  from  our  worst 
stocks.  Eugenists  are  agreed  that  the  greatest  need 
is  for  some  method  of  adjusting  conditions,  so  as  to 
remove  this  menace  to  the  future  of  the  race. 

The  Problems  of  Population. 

Problems  of  population  have  been  discussed  ever 
since  Malthus  formulated  his  law  that  population 
tends  to  increase  in  geometrical  ratio,  while  the  means 
of  living — food  and  raiment  based  on  agriculture — 
only  increase  in  arithmetical  ratio,  thus  leading  to 
human  poverty,  misery,  and  vice.  The  accuracy  of 
this  law  has  often  been  affirmed  and  as  often  denied. 
The  fact  that  it  led  both  Darwin  and  Wallace  inde- 
pendentl}'    to    the    conception    of    natural    selection 


SOCIAL  AND  WORLD  ASPECTS  241 

certainly  stands  to  its  credit.  It  does  not  follow, 
however,  that  the  law  is  quantitatively  accurate  as 
stated,  and  it  is  in  this  direction  that  it  has  broken 
down  in  recent  3'ears.  In  the  meantime  the  law  of. 
diminishing  returns  has  been  recognised  as  applying 
both  to  agriculture  and  industry. 

The  whole  problem  of  population  has  recently  been 
discussed  by  Carr-Saunders  (1922)  in  a  broadminded 
and  restrained  manner,  and  we  may  first  give  a  short 
summary  of  the  facts  and  arguments  he  presents.  He 
points  out  that  the  fecundity  of  man  has  increased 
in  comparison  with  that  of  primitive  peoples.  In  this 
man  agrees  with  cultivated  plants  and  domesticated 
animals  generally.  Civilised  man  creates  a  reserve, 
not  only  for  himself,  but  for  his  domesticated  animals 
and  plants,  which  enables  them  to  function  as  a  more 
prolific  reproducing  mechanism.  This  increased 
fecundity  is  due  to  more  food  and  better  conditions 
of  life.  In  primitive  races  the  number  of  children 
reared  in  a  family  is  usually  two  to  four,  or  sometimes 
six.  Some  tribes  bring  up  only  two  children  per 
famil}'.  Artificial  abortions  are  frequent,  and  in- 
fanticide universal.  Child  mortality  is  high,  owing 
to  the  hard  conditions  and  lack  of  suitable  food. 
The  period  of  lactation  often  lasts  two  years  or  more, 
sometimes  five  or  six  years,  or  even  longer.  Under 
these  conditions  births  are  fewer  than  in  many 
civilised  families,  and  survivals  fewer  still,  the  popula- 
tion tending  to  remain  stationary  in  numbers  over 
long  periods.* 

The  view  of  Malthus  that  the  means  of  subsistence 
can  only  increase  in  arithmetical  ratio,  has  long  been 
disproved  by  statistics.  On  this  point  his  argument 
collapses,  for  it  is  seen  that  the  arithmetical  ratio 
only  holds   so    long   as    there   is    no    advance  in  skill 

*  Darwin  first  directed  attention  to  these  and  similar  facts  in 
his  Descent  of  Man. 

16 


242  HEREDITY  AND  EUGENICS 

or  improvement  of  methods.  But  the  history  of 
civiKsation  has  consisted  in  just  such  advances,  which 
lead  in  each  case  to  a  corresponding  increase  in  yield 
for  a  given  amount  of  labour.  The  law  of  diminishing 
returns,  however,  limits  this  3^ield,  both  in  agriculture 
and  in  industry.  This  leads  Carr-Saunders  to  the 
important  conception  of  an  optimum  number,  which 
he  states  in  the  following  words  (p.  200):  "  Since  the 
laws  in  general  are  applicable  to  all,  there  will  be, 
taking  into  account  on  the  one  hand  the  known  arts 
of  production,  and  on  the  other  hand  the  habits  and 
so  on  of  the  people  at  any  one  time  in  an}'  given  area, 
a  certain  density-  of  population  which  will  be  the  most 
desirable  from  the  point  of  view  of  return  per  head  of 
population.  There  will,  in  fact,  under  any  circum- 
stances always  be  an  optimum  number."  If  the 
population  is  either  above  or  below  that  number, 
the  return  per  head  will  be  less.  For  an}'  country 
there  is,  then,  an  optimum  population  corresponding 
to  its  agricultural  and  climatic  conditions  and  in- 
dustrial development.  Increase  in  skill  brings  an 
increasingly  dense  population  and  a  larger  income 
per  head,  and  so  long  as  skill  increases  the  optimum 
density  of  population  will  go  on  increasing.  To 
Malthus  the  problem  was  one  of  the  relative  rate  of 
increase  of  population  and  food  production.  With 
the  conception  of  an  optimum,  it  is  one  of  densit}'  of 
population  and  the  productiveness  of  industry. 

An  optimum  number,  if  attained  in  a  population, 
implies  the  maintenance  of  a  standard  of  living.  This 
number  appears  to  be  usually  approached,  both  among 
primitive  tribes  and  in  civilised  countries.  The 
optimum  will  mean  greater  or  less  density  of  popula- 
tion, according  to  the  fertility  of  the  country  in  the 
broadest  sense  and  the  skill  or  degree  of  civihsation 
of  its  people.  In  a  poor  country  like  Patagonia, 
inhabited   by  a   primitive   tribe,   the   optimum   con- 


SOCIAL  AND  WORLD  ASPECTS  243 

ditions  may  be  represented  by  the  present  very  sparse 
population.  In  a  country  like  Belgium,  where  in- 
tensive agriculture  and  industry  can  be  practised  by 
an  intelligent  people,  the  present  dense  population 
may  still  represent  the  optimum.  It  is  believed  that 
many  parts  of  India  and  China  are  over-populated, 
and  the  same  was  true  of  Ireland  about  i  585.  Under 
these  conditions  the  people  lose  their  standards  of 
living,  and  multiply  up  to  the  limits  of  subsistence. 
Such  a  loss  of  standards  may  result  from  fear, 
oppression,  repeated  plagues,  or  similar  conditions. 

The  author  points  out  that  the  fecundity  of  all 
animal  species  will  tend  to  be  regulated  by  natural 
selection.  "  A  limit  is  set  to  the  development  of 
the  strength  of  fecundit}"  be3'ond  a  certain  point  by 
the  fact  that  it  cannot  be  to  the  advantage  of  any 
species  that  its  fecundity  should  increase  considerably 
be3^ond  the  point  which  ensures  the  survival  of  the 
species,  as  such  an  increase  w^ould  intensify  the  struggle 
between  the  members  of  the  species — this  intensifica- 
tion of  the  struggle  not  bringing  any  corresponding 
advantages."  Man  inherited  from  his  pre-human 
ancestor  a  higher  fecundit}^  than  he  needs.  His 
development  of  intellect  enabled  him  to  circumvent 
or  overcome  the  animals w^hich  preyed  on  his  ancestors. 
In  this  way  he  lessened  his  own  death-rate,  but  his  in- 
telligence enabled  him  at  the  same  time  to  overcome 
his  high  fecundity  by  infanticide  and  other  means. 
He  thus  escaped  the  disadvantages  which  would  have 
come  from  too  high  fecundity — a  natural  fecundity 
w^hich  would  otherwise  have  ultimatelv  been  reduced 
by  selection. 

That  a  standard  of  living  exists  among  primitive 
peoples  is  shown  by  many  features  of  primitive  life — 
for  example,  by  the  fact  that  the  young  men  are 
made  to  reach  a  certain  standard  of  skill  and  attain- 
ment before  they  can  marry.     In  the  Middle  Ages 


244  HEREDITY  AND  EUGENICS 

and  later  the  system  of  apprenticeships  of  the  gilds 
had  similar  effects.  Definite  laws  also  prevented 
the  poor,  vagabonds,  and  Twastrels  from  marrying. 
The  more  or  less  unconscious  intention,  as  well  as  the 
result  of  such  social  regulations,  w^as  to  maintain  the 
population  near  the  optimum  by  delay  of  marriage 
until  a  certain  standard  was  reached,  and  also  to 
limit  reproduction  on  the  part  of  those  least  fit  in  a 
social  sense.  There  are  now  no  corresponding  restric- 
tions on  the  marriage  of  the  wage-earning  classes, 
with  the  result  that  they  soon  attain  their  maximum 
income  and  marry  earlier  than  the  professional  classes, 
whose  maximum  earning-power  comes  much  later  in 
life.  Maternity  benefits  and  doles  furnish  a  further 
incentive  to  multiply.  It  is  probable  that  the  re- 
sulting tendency  to  increase  in  numbers  out  of  due 
proportion  to  higher  classes  has  the  effect  of  lowering 
the  standard  of  living  of  the  working  classes,  because 
it  is  a  phenomenon  of  over-population.  Here  we 
see  how  questions  of  quality  and  quantity  of  popula- 
tion are  inextricabty  interwoven. 

Carr-Saunders  considers  that  populations  have 
normally  been  stable  throughout  human  history,  and 
that  rapid  increase  in  numbers  is  the  exception.  In 
England,  during  the  period  1 880-1 91 3,  the  average 
income  per  head  increased  from  100  to  134  in  real 
wages.  Hence  there  was  no  over-population  in  the 
country,  as  a  whole,  during  this  period  of  rapid 
growth  in  population.  From  1840  to  1880  the  birth- 
rate remained  stationary.*  Then  the  decline  set  in, 
and  the  birth-rate  dropped  gradually  to  about  two- 
thirds  its  former  value.  This  decline  is  regarded  as 
a  response  to  economic  conditions,  the  earlier  rapid 
rate   of  increase   having   ceased   to   be   economicalh^ 

*  According  to  Dean  Inge,  between  1800  and  1900  the  popula- 
tion of  England  increased  300  per  cent.,  while  it  only  increased 
30  per  cent,  between  1700  and  1800. 


SOCIAL  AND  WORLD  ASPECTS  245 

advantageous.  The  decline  is  believed  to  have  taken 
place  first  in  the  higher  classes,  because  they  respond 
more  quickly  to  a  change  in  economic  conditions. 
It  is  viewed  with  considerable  equanimity,  even  as 
regards  its  differential  character,  confined  as  it  is 
chiefly  to  the  upper  and  middle  classes,  the  latter, 
through  selection,  including  the  great  majority  of 
the  best  elements  in  the  community.  Other  wTiters 
take  a  much  more  serious  view  of  this  matter,  and 
apparently  wdth  good  reason.  It  seems  clear,  for 
instance,  that  in  the  United  States  the  Anglo-Saxon 
stock  is  failing  to  hold  its  own  (see,  for  instance, 
Holmes,  1921),  and  this  is  particularl}-  true  of  the 
more  highl}^  trained  graduates  of  the  Universities. 
Similarly  in  England  the  decline  in  the  birth-rate 
since  the  'eighties  has  occurred  chiefly  in  the  elements 
of  the  population  whose  inheritance  is  most  valu- 
able to  the  nation.  Once  a  particular  stock  having 
exceptional  qualities  is  lost  it  is  ver}-  questionable 
whether  it  can  ever  be  replaced .  The  history  of  Greece 
and  Rome  and  other  decayed  nations  shows  that  once 
a  human  stock  has  disappeared,  for  whatever  reason, 
it  is  gone  for  ever.  An  obvious  duty  rests  upon  the 
most  highly  endowed  members  in  all  ranks  of  society 
to  perpetuate  their  kind. 

Before  leaving  the  subject  of  quantity  in  popula- 
tion, we  ma}^  refer  to  some  recent  results  on  the 
question  of  population  growth.  Pearl  and  Reed 
(1920)  have  applied  a  logarithmic  formula  to  the 
growth  of  population  in  the  United  States  since  1790, 
and  they  conclude  that  the  ultimate  population  of 
that  country  will  not  exceed  197  millions — i.e.,  less 
than  double  the  present  population.  East  (1920, 
1 921),  from  a  consideration  of  the  agricultural 
possibilities  of  the  country,  concludes  that  there  are 
about  800  million  acres  of  arable  land.  If  the  popula- 
tion limit  were  placed  at  2-5  acres  per  man,  which  is 


246  HEREDITY  AND  EUGENICS 

comparable  with  present  conditions  in  France  and 
Germany,  this  would  lead  to  a  figure  of  320  millions, 
to  which  would  be  added  1 1  millions  supported  on 
the  grazing  lands  and  forests.  A  total  of  331  millions 
would  thus  be  the  maximum  conceivable  under  any- 
thing like  the  present  conditions  of  living.  Long 
before  any  such  density  of  population  is  reached, 
the  younger  countries  would  have  ceased  to  be  food- 
exporting,  and  each  country  would  have  to  be  self- 
supporting  in  this  regard.  But  it  is  ver}^  doubtful 
if  the  American  population  will  ever  reach  such  a 
figure.  These  problems  of  racial  movements  and 
population  increase  are,  however,  beyond  our  present 
purview,  and  can  only  be  touched  upon  here. 

Population  and  Quality 

Among  primitive  races  natural  selection  and 
differential  fertility  act  so  as  to  tend  to  preserve 
existing  types,  rather  than  to  bring  about  further 
evolution.  The  same  appears  to  be  true  of  wild 
species  in  nature  generally.  Under  fixed  conditions 
they  tend  to  remain  stable,  any  unfavourable  aberrant 
types  being  cut  off  as  they  appear.  But  any  kind  of 
change  in  the  conditions  initiates  readjustments  in 
which  selection  may  favour  a  different  type,  and 
various  processes  of  modification  may  be  set  in 
motion.  This  must  apply,  at  any  rate,  to  the  de- 
velopment of  adaptations,  though  it  apparently  does 
not  apply  to  many  mutations. 

As  regards  the  history  of  man's  peculiarly  human 
qualities,  it  may  be  the  case  that  progress  in  intel- 
lectual capacity  came  largely  before  progress  in  skill. 
But  this  evolutionary  chapter  of  man's  intellectual 
development  remains  mostly  to  be  written.  Granted 
the  striking  facts  of  the  large  cranial  capacity  of  early 
human  races  and  species,  the  reasons  for  this  develop- 


SOCIAL  AND  WORLD  ASPECTS  247 

ment  and  the  conditions  under  which  it  took  place 
remain  obscure.  However  this  transitional  phase 
from  man's  prehuman  ancestor  took  place,  a  new  era 
began,  at  least  as  early  as  the  Lower  Palaeolithic, 
in  which  tradition  began  to  play  the  most  impor- 
tant role  in  man's  subsequent  development.  Carr- 
Saunders  rightly  emphasises  the  value  of  tradition 
and  its  great  importance  in  the  evolution  of  civilisa- 
tion. He  concludes — and  the  majority  of  anthro- 
pologists would  apparently  agree  with  him — that 
''  the  major  part  of  the  progress  in  the  evolution  of 
the  intellectual  faculties  had  been  accomplished  far 
back  in  Palaeolithic  times."  The  artistic  and  cultural 
achievements  of  Palaeolithic  man  certainly  appear  to 
support  this  view,  although  the  more  artistic  produc- 
tions belong  to  the  late  Aurignatian  and  Magdalenian 
periods  of  the  Upper  Palaeolithic.  And  yet  we  believe 
he  pushes  this  conception  too  far  when  he  states  that 
modern  races,  representing  the  Palaeolithic  culture 
level,  differ  from  modern  Europeans  in  disposition 
rather  than  in  intellect. 

It  is  true  that  observers  of  the  children  of  native 
races  find  that  as  beginners  at  school  the}^  are 
frequently  as  keen,  or  even  keener,  than  the  children 
of  whites.  But  their  mental  development  ceases 
early.  Like  the  feebleminded,  they  show  arrested 
mental  development.*  In  their  native  surroundings 
their  activities  may  be  diverted  to  other  matters  by 
the  traditions  of  their  fathers.  This,  however,  can 
hardly  be  said  of  the  negroes  transplanted  to  America 
and  living  in  the  midst  of  civilised  traditions,  yet  the 
descendants  of  these  negroes  in  the  present  generation 
are  shown  to  be  inferior  to  white  children  of  corre- 
sponding age  in  ever}'  stage  of  their  development. 
Evidently  primitive  peoples  are  often  lacking  in  the 
capacity    for    perseverance.     Their    lives    frequently 

*  For  a  different  view,  see  p.  248. 


248 


HEREDITY  AND  EUGENICS 


consist  of  periods  of  violent  adventure  and  exertion  in 
war  or  the  chase,  alternating  with  periods  of  qui- 
escence. The  capacity  for  perseverance  is  one  of  the 
later  acquisitions  of  civilised  man. 

It  is  therefore  difficult  to  follow  Carr-Saunders  in  his 
statement  (p.  397),  that  "  there  seems  to  be  no  marked 
difference  in  innate  intellectual  power  "  between 
negroes  and  modern  Europeans.  All  the  evidence, 
in  fact,  points  to  the  contrar}'  conclusion,  but  he 
ascribes  this  to  differences  merely  in  disposition  and 
temperament.  The  same  t3'pe  of  argument  might 
apply  equall}'  well  to  the  feebleminded.*  As  already 
pointed  out  (p.  226),  the  example  of  the  Japanese, 
who  have  quickly  picked  ujd  modern  science  and 
industr}',  in  contrast  with  the  many  primitive  races 
who  are  obviously  incapable  of  doing  so,  is  a  sufficient 
answer  to  the  belief  that  the  diiference  involved  is  one 
mereh'  of  temperament  and  not  of  intellectual  ability. 
This  fact  is  sufficient  to  show  the  great  gap  in  intel- 
lect which  exists  between  the  Japanese  and  really 
primitive  peoples. 

Granting,  therefore,  the  great  importance  of 
tradition  in  accumulating  and  handing  on  by  means 
of  contact,  suggestion,  and  language  the  accumulated 
skill  of  civilised  man,  3^et  there  must  have  been  also 
in  connection  with  this  process  an  increase  of  brain- 
power on  the  part  of  man  himself.  This  must  have 
taken  place  since  Palaeolithic  times,  although  it  is  not 
clear  how  it  came  about,  considered  as  an  evolutionar}' 
process.  Concomitant  with  this  process  went  on  the 
differentiation  of  society  from  its  primitive  beginnings, 
in  which  all  the  units  or  clans  were  alike — the  so- 
called  segmentar}^  social  condition  which  persists  in 

*  McDougal  (192 1)  refers  to  the  fact  that  the  negro,  whether 
living  in  Africa,  Malaysia,  the  West  Indies,  North  or  South 
America,  continues  to  show  the  same  fundamental  ph^^sical  and 
mental  qualities. 


SOCIAL  AND  WORLD  ASPECTS  249 

native  races — to  the  highl}'  differentiated  or  organic 
condition  of  civilised  society,  in  which  a  great  variety 
of  professions  and  occupations  exist,  and  men  are 
grouped  according  to  their  professions  and  not 
according  to  their  descent.  Carr-Saunders  points  out 
that  with  increasing  contact  between  men  perform- 
ing the  same  functions,  as  populations  increased  in 
density,  the  segmentary  type  of  social  organisation 
necessarily  gave  place  to  the  organic  type,  with  the 
final  result  that  modern  human  society  has  the  highly 
differentiated  and  integrated  structure  and  activities 
of  a  complex  organism. 

Another  point  on  which  we  feel  it  necessary  to 
differ  from  Carr-Saunders  in  his  able  analysis  of  the 
part  tradition  has  played  in  the  mental  evolution  of 
man  is  with  regard  to  the  differences  between  classes 
in  the  same  society.  He  concludes  that  the  direction 
and  degree  in  which  the  intellect  works  is  very  largel}^ 
determined  by  tradition,  and  that  profound  differences 
in  tradition  between  the  classes  of  modern  society 
account  for  most  of  the  mental  differences  manifested. 
Here,  again,  we  believe  he  la3^s  too  much  stress 
on  tradition.  A  ver}'  considerable  proportion  of 
exceptional  men  break  entirel}^  with  tradition  in 
choosing  their  life  work.  The  author  admits  that 
the  children  of  the  professional  classes  are  on  the 
average  two  years  in  advance  of  the  children  of 
unskilled  labourers,  and  hence  show  superior  intel- 
ligence. Similarly,  McDougal  (1921)  quotes  results 
of  observations  on  school-children  in  Pittsburg, 
indicating  a  marked  association  between  economic 
status  of  the  parents  and  school  advancement  or 
intelligence  of  the  children.  Yet  Carr-Saunders  con- 
cludes that  there  are  only  slight  differences  in  intel- 
lectual capacity  between  the  classes.  McDougal,  on 
the  contrary,  emphasises  the  dangers  associated  with 
the  differential  birth-rate  which  has  grown  up  during 


250  HEREDITY  AND  EUGENICS 

the  last  half-century,  and  points  out  that  the  longer 
the  social  ladder  has  been  at  work  passing  up  the 
exceptional  members  of  the  lower  strata  of  society 
to  the  higher,  the  greater  will  become  the  innate 
germinal  differences  between  classes.  When  this 
condition  is  accompanied  by  a  failure  of  the  higher 
strata  to  reproduce  themselves,  then  it  is  obvious  that 
the  germinal  reserves  of  abilit}^  in  the  lower  classes 
are  being  gradually  depleted  and  exhausted.  This 
can  only  mean  a  permanent  loss  of  power  and  ability 
to  the  race  in  which  it  occurs.  Already  McDougal 
sees  clear  indications  of  this  exhaustion  in  the 
decreasing  numbers  who  are  passing  up  the  ladder 
during  the  present  generation.  Britain  seems  to  have 
gone  further  in  this  direction  than  any  other  country 
in  the  depletion  of  its  stocks  showing  leadership  and 
ability,  although  it  is  not  clear  that  the  United  States, 
with  its  great  numbers  of  low-class  immigrants 
replacing  the  Anglo-Saxon  stock  in  various  parts  of 
the  countr}^,  is  in  any  better  case.  These  people 
may  absorb  the  tradition  of  their  predecessors  in  a 
generation  or  two,  but  it  is  certain  that  they  cannot 
absorb  their  germinal  qualities,  nor  alter  those  which 
are  already  present  in  their  own  germ  plasm. 

The  problems  envisaged  in  the  last  few  paragraphs 
have  been  so  much  written  about  in  recent  vears 
that  we  do  not  propose  to  discuss  them  further  here. 
They  remain  at  the  heart  of  all  questions  of  racial 
improvement  through  eugenic  ideals.  The  problem 
of  formulating  laws  which  would  foster  an  increase 
in  the  more  efficient  and  desirable  members  in  each 
stratum  of  society  would  seem  almost  to  surpass  the 
wit  of  man,  and  so  far  as  w^e  know,  it  has  not  3^et 
been  successfully  accomplished  in  any  community. 
The  task  appears  all  the  more  appalling  when  it  is 
remembered  how  frequently  Parliamentary  laws  have 
an  economic  effect  quite  different  from  that  antici- 


SOCIAL  AND  WORLD  ASPECTS  251 

pated  or  intended.  Probably  an  intelligent  and  en- 
lightened public  opinion  is  more  efficacious  than  any 
laws  that  could  be  devised.  And  a  large  element  of 
that  enlightenment  will  consist  in  an  understanding 
of  the  nature,  the  laws,  and  the  ubiquity  of  heredity. 
However,  an  obvious  negative  measure  which  can 
be  carried  into  effect  is  the  prevention  of  reproduction 
on  the  part  of  undesirables,  such  as  the  feebleminded. 
Such  measures  are  necessary,  not  so  much  for  the 
improvement  of  the  race,  as  for  arresting  its  rapid 
deterioration  through  the  multiphcation  of  the  unfit. 


nOPEKTT  UBKART 


LIST  OF  GENERAL  WORKS  BEARING 

ON   EUGENICS 

Babcock,  E.  B.,  and  Clausen,  R.  E.  Genetics  in  Relation  to 
Agriculture.  1918.  London  and  New  York:  Hill  Publishing 
Co.     Pp.  675,  figs.  239,  pis.  4. 

Bateson,  W.  Mendel's  Principles  of  Heredity.  1913.  Cam- 
bridge Press.     Pp.  413,  figs.  39. 

Carr-Saunders,  a.  M.  The  Population  Problem.  1922.  Oxford 
Press.     Pp.  516. 

Castle,  W.  E.  Genetics  and  Eugenics.  1916.  Harvard  Univer- 
sity Press.     Pp.  357,  figs.  135. 

Davenport,  C.  B.  Heredity  in  Relation  to  Eugenics.  London: 
Williams  and  Norgate.     Pp.  298. 

Doncaster,  L.  An  Introduction  to  the  Study  of  Cytology.  1920. 
Cambridge  Press.     Pp.  280,  figs.  31,  pis.  24. 

Galton,    F.     Hereditary    Genius.      1869.     London:    Macmillan. 
Second  Edition,  reprint,  1914.     Pp.  390. 
Inquiries  into  Human  Faculty  and  its  Development.      1883. 

London:  Macmillan.     Pp.  387,  pis.  5. 
Natural  Inheritance.      1889.     London:  Macmillan.     Pp.259. 

Gates,  R.  Ruggles.  The  Mutation  Factor  in  Evolution.  1915. 
London:  Macmillan.     Pp.  353,  figs.  114. 

Goddart,  H.  H.  Feeblemindedness,  Its  Causes  and  Conse- 
quences.     1914.     New  York:  Macmillan.     Pp.  599. 

GuYER,  M.  F.  Being  Well-Born.  1916.  Indianapolis:  Bobbs- 
Merrill  Co.     Pp.  374,  figs.  39. 

Inge,  W.  R.  Outspoken  Essays.  1919.  London:  Longmans. 
Pp.  281. 

McDougal,   Wm.   Psychology,   the  Study  of  Behaviour.      191 9. 

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An    Introduction    to    Social    Psychology.      1919.     London: 

Methuen.  Fourteenth  Edition.  Pp.  459. 
National    Welfare    and    National    Decay.     1921.     London: 

Methuen.     Pp.  214. 

252  - 


LIST  OF  GENERAL  WORKS  253 

Morgan,  T.  H.  The  Physical  Basis  of  Heredity.  1919.  Phila- 
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Pearson,  Karl,  and  Collaborators.  Treasury  of  Human  In- 
heritance. 

Plate,  L.  Tererbungslehre,  mit  besonderer  Beriicksichtigung  des 
Menschen,  fiir  Studierende,  Arzte  und  Ziichter.  191 3. 
Leipzig:  W.  Engelmann.     Pp.  519,  figs.  179,  pis.  3. 

PoPENOE,  Paul,  and  R.  H.  Johnson.  Applied  Eugenics.  1920. 
New  York:  Macmillan.     Pp.  459,  figs.  46. 

PUNNETT,  R.  C.  Mendelism.  1919.  Fifth  Edition.  London: 
Macmillan.     Pp.  219,  figs.  52,  pis.  7. 

Shand,  a.  F.  The  Foundations  of  Character,  being  a  Study  of 
the  Tendencies  of  the  Emotions  and  Sentiments.  1920, 
London:  Macmillan.     Pp.  578. 

Tansley,  a.  G.  The  New  Psychology  and  its  Relation  to  Life. 
1920.     London:  Geo.  Allen  and  Unwin.     Pp.  283,  figs.  10. 

Watson,   J.    B.     Behaviour:  An   Introduction    to    Comparative 
Psycholog3^      1914-     New    York:    Henry   Holt    and    Co 
Pp.  439,  figs.  70. 
Psychology  from  the  Standpoint  of  a  Behaviourist.      1919. 
Pp.  429,  figs.  66. 

Wilson,  E.  B.  The  Cell  in  Development  and  Inheritance.  1906. 
London  and  New  York:  Macmillan.     Pp.  483,  figs.  194. 


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17 


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(From  Bot.  Abstr.,  x.  86,  1922.) 


270  HEREDITY  AND  EUGENICS 

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Seligman,  C.  G.  a  Note  on  Albinism,  with  Special  Reference  to 
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Sessions,  Mina  A.  Feebleminded  in  Ohio.  Journ.  Hered.,  191 7, 
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Shattock,  S.  G.,  and  Seligman,  C.  G.  An  Example  of  True 
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INDEX 


Aberystwith,  ioi 

Abietineae,  polyembryony  in,  179 

Ability,  and  brain,  234 

inheritance  of,  145,  147,  148, 
170,  222 
Abnormal  segmentation  of  fingers, 

Abnormalities,  inheritance  of,  75, 
76,  106,  116,  125,  127,  129, 
142,  158,  174 
occurrence  of,  93,  204 
Abortions  in  primitive  races,  241 
Absence    of     external    ear,     133, 

134 
of  patella,  136 

Acanthosicyos  horrida,  227 
Achondroplasia,    34,    35,    39,    40, 

126,  215 
Acromegaly,  211,  216 
Addison's  disease,  212 
Adkinson,  June,  138 
Adrenal     capsules.     See     Supra- 
renal capsules 
Adrenalin,  217,  218,  220 
Agriculture,  241,  242 
Ailments  of  twins,  188 
Aino  of  Japan,  54 
Albert,  Henry,  93 
Albinoes,  eyeballs  of,  44 
Albinism,    change    in    hereditary 
behaviour  of,  70 

frequency  of,  65 

in  animals,  68 

in  cattle,  69 

in  guinea-pigs,  125 

inheritance  of,  57,  6y,  no 

in  horses,  71 

in  rabbits,  125 
Albinotics,  58,  65,  68 
Alcohol,  effect  on  germ  cells,  92 
Alcoholism,  142,  149,  153,  235 
Alexander,  103 
Alkaptonuria,  no 
Allelomorphs,  multiple,  27 


Alpine  race,  212,  231 
Amaurosis,  117,  120,  142,  158 
Amblystoma,  41 
American  army  intelligence  tests, 

234 
Americans  in  crosses,  230 
Amerindians,  10 1 
Amphibians,    hermaphrodites   in, 

133 
Amphioxus,  210 

Analysis  of  the  mind,  146 

Ancestral  inheritance  in  man,  209 

Ancon  sheep,  40 

Anencephali,  193 

Angioneurotic  oedema,  127 

Angora  hair,  in  guinea-pigs,  1 5 

in  other  animals,  125 

Animal  behaviour,  165 

Aniridia,  116,  120,  130 

Anodont  condition,  71 

Anthropoid    apes,    behaviour    of, 

165 

hormones  in,  217 

Antibody,  144 

Antisocial  behaviour,  163 

Apache   Indians,   left-handedness 

in,  72 

Apes,  placenta  of,  1 78 

Apogamy,  209 

Apprenticeships,  244 

Arable  land  in  the  United  States, 

245 
Arabs,  Polydactyly  in,  loi 

Arboreal  ancestry  of  man,  17S 

Arctomys,  68 

Arey,  L.  B.,  199 

Argentine,  crosses  in,  230 

Aristocratic  society,  221 

Aristotle,  98 

Arizona,  39,  65 

Armadillo,  scutes  of,  181,  19^ 
I  young  of,  176,  177,  17S,  iSi, 

182,  199,  200 

Arrested  development,  89,  i  54 

Arsenic,  in  thyroxin,  214 
1    Artificial  selection,  175 

273  t8 


2  74 


HEREDITY  AND  EUGENICS 


Artistic  ability,  inheritance  of,  1 70 

evolution  of,  247 
Assortative  mating,  139,  208 
Astlima,  inheritance  of,  138,  188 
Astigmatism,  inheritance  of,  116 
Ataxia,  in  pigeons,  109,  167 
Ateliosis,  34,  35,  39 
Atrichosis,  56 
Atwood,  E.  S.,  loi 
Aurignatian  man,  247 
Australian    aborigines,    mentality 
of,  225 
stature  of,  28 
Austria,  albinoes  in,  65 
Austrians  in  crosses,  230 
Autonomic  bodily  functions,  166 
Auximones,  42 

B 

Bach  family,  1 70 
Bailey,  P.  G.,  31 
Baker,  Henry,  121 
Balanced  lethal  factors,  209 
Baldness,  inheritance  of,  25 
Baldwin,  'ji 

Ballowitz,  E.,  loi,  103,  104 
Banta,  A.  M.,  132 
Bantams,  silver  seabright,  31 
Bantus,  abnormalities  in,  71 
crosses  with  Boers,  228 
Barfurth,  96 
Barrington,  Amy,  34 
Bartlett,  H.  H.,  42 
Bateson,  W.,   75,  84,  95,  97,  98, 

no,  113,  115,  124,  205 
Bauhin,  131 
Beagle  voyage,  169 
Bean,  R.  B.,  53 
Beans,  bush  varieties,  35     • 

pure  lines  in,  221 
Bear,  albino,  69 
Beavers,  albino,  68 
Beel^y,  A.  L.,  72,  -ji,  74 
Behaviourism,  165 
Belgium,  population  in,  243 
Bergen,  Norway,  48 
Bergman,  E.,  108 
Beri-beri,  42 

Berman,  Louis,  215,  218,  219 
Bermuda,   52 
Bernstein,  C.,  133 
Bilateral  asymmetry,  inheritance 

of,  191 
Bimanual  synergia,  136 
Binet- Simon,  tests,  T46,  149,  154, 

232,  234  ' 

Biolobed  ear,  inheritance  of,  135 
Biometry,  9 


Biovular  twins,  191.      See  Twins 
Bipinnaria  larva,  179 

embryology  of,  177 
Birds,  eye  colours  in,  50,  5 1 
Birth-rates,    205,    237,    238,    239, 

240,  244 
Blacker  and  Lawrence,  131 
Blastocyst,  of  armadillo,  177 

of  deer,  178 
Blastogenic  variation,  181 
Blazek  twins,  1 79 
Bleeders.     See  Haemophilia 
Blending    inheritance,    167,    213, 

223 
Blindness,  hereditary.    See  Amau- 
rosis 
Blood  system,  peculiarities  in,  137 
Blood  transfusion,  129 
Blue  eyes  in  Nordic  race,  2 1 2 
inheritance  of,  45 
in  the  tropics,  207 
sclerotics,  inheritance  of,  142 
Boas,  H.  M.,  44 
Boas,  J.  E.  v.,  96 
Bodily  effects  of  anger,  2 1 8 
Boers,  crosses  of,  229 
Bohemia,  179 
Bokhara,  sheep  of,  135 
Boleyn,  Anne,  loi,  102 
Bollenbach  family,  5  5 
Bonavia,  E.,  93 
Bond,  C.  J.,  49,  50,  54,  95 
Bonnevie,  K.,  96,  194 
Borneo,   103 
Boston,  39,  40 
Bottomley,  W.  B.,  42 
Bovidffi,  224 
Bowditch,  H.,  113 
Brachycephalic  skulls,  212 
Brachycephaly,  proopic,  126,  216 
Brachydactyly,  9,  10,  11,  12,  75, 
78,  84,  89,  104,  174,  197 
in  fowls,  92 
Brachyphalangy,  90,  91 
Brachysm,  35 
Brains  of  twins,  186 

of  ataxic  pigeons,  109 
of  negro,  233 
Branchial  fistula,  130 
Brazil,  65,  237 
Briggs,  H.  H.,  116 
Brightness  and  intelligence,  i  57 
British  Columbia,  Indians  of,  65 
Brittle  bones,  inheritance  of,  75, 

142 
Bronchial  asthma,  inheritance  of, 

138,  188 
Bronchitis,  138 
Brooks,  W.  K.,  7 


INDEX 


275 


Bryant,  F.  A.,  141 

Bryn,  45 

Buenos  Ayres,  230 

Bulloch,  W.,    IK),    114,    127,    128, 

131 
Bullosa,  inheritance  of,  128 

Bury  St.  Edmunds,  61 

Bush  varieties  of  vegetables,  35 


Cacogenic  matings,  160 
Caesar  in  Gaul,  239 

personality  of,  220 
Caesar's  horse,  96,  97 
CaesarotOmy,  34 
Calcar  loop,  inheritance  of,  176 
Calliphora  eryihrocephala,  114 
Cambridge,  94 
California,  39,  146,  157,  178 
Cancer,  123,  140,  141 
Canidae,  variation  in,  125 
Cannon,  W.  B.,  217,  218 
Cape  Cod,  65 
Capion,  Abbe,  1 14 
Carlisle,  Anthony,  104 
Carmichael,  W.  J.,  98 
Carnivora,  multiple  births  in,  200 
Carrel,  41 
Carr  Saunders,  225,  226,  240,  241, 

242,  244,  247,  248,  249 
Caste  in  society,  221 
Castle,  W.  E.,  28,  29,  30,  31,  32, 

T,Z,  50,  63,  94.  i6s 
Cataract,  75,  no,  m,  116 
Catlin,  65 

Caton,  Dr.  John  D.,  39 
Cats,  on  Sable  Island,  37 

Polydactyly  in,  93 
Cattle,  albino.  69 

cancer  of  eye  in,  140 

cataract  in,  in 

cretins  in,  216 

interfertility  in,  224 

intoxication  by  pampas  grass, 
167 

notch  in  ear  of,  135 

on  Sable  Island,  36,  37 

Polydactyly  in,  97 

prognathism  in,  125 

sterility  in,  196 

twin  births  in,  198,  202,  203 
Caucasians,  loi,  212,  215,  231 
Causes  of  death,  237 
Celosia,  fasciation  in,  5 
Cephalic    index,    inheritance    of, 

145 
Cereals,  seedlings  of,  74,  175 

Cerebro-spinal  meningitis,  153 


Character,  defined,  148 

and  handwriting,  172 
Chartley  herd  of  cattle,  70 
Cheek,  one  bigger,  inherited,  i  3O 
Child,  4 
Children  of  native  races,  241,  243, 

247 
Chillingham  cattle,  70 
China,  over-population  in,  243 
Chinese,  hair  of,  53 

in  crosses,  230 

Polydactyly  in,  loi 

ponies,  35,  126 

race,  215 
Chipmunks,  albino,  68 
Chiriguan  Indians,  30 
Choice  of  ideals,  148 
Chorea,  chronic,  156 
Chorion,  199 

fusion  in  cattle,  201,  202 
Chromosomes,  accessory,  20 

and  phylogeny,  21 

explained,  13,  14,  15 

in  heredity,  16,  24 

in  man,  20,  22,  209,  210 

of  wheat,  22 

sex,  19,  20 
Civilization,    causes    of   downfall, 
238,  239 

measure  of,  205 
Cladocera,  sex  intergrades  in,  132 
Clasping  the  hands,  74 
Cleft  palate,  1 30 
Cleppie  Bells,  yj 
Climate  and  population,  242 
Clonic     spasms    in     guinea    pigs, 

167 
Coburn,  C.  A.,  167 
Cockayne,  E.  A.,  61 
Colborn,  Zerah,  104 
Cole,  L.  J.,  112,  167 
Colmar,  55 
Coloboma,     inheritance  of,     116, 

120, 130 
Colour-blindness,  19,  22,  24,  no, 
112,  113,  114,  115 

in  Europe,  1 13 
Colour  varieties  of  mankind,  212 
Columba  livia,  50 

cenas,  50 
Compton,  R.  H.,  72,  74,  75 
Conard,  H.  S.,  75 
Conklin,  E.  G.,  72 
Constricted  eyelids,  109 
Convicts,  British,  140 
Cook,  O.  F.,  35 
Cornea,  degeneration  of,  116 

nodular  opacity  of,  116 
Corns,  5 


2^6 


HEREDITY  AND  EUGENICS 


Corpora  lutea,  177,  178,  196,  200 

quadrigemina,  211 
Correlation-coefficients,  28,  30,  32, 

139,  140,  145,  146,  185,  209 
Cortez,  65 

Cotton,  short  internodes  in,  35 
Cragg,  E.,  90 

Cranial  capacity  of  early  man,  246 
Cretin,  babies,  216 

cattle,  216,  217 
Crew,  F .  A .  E . ,  sex  of  frogs,  132 
Criminals  and  inheritance,  163 

classification  of,  184 

feebleminded,  149 
Crooked  little  finger,  193 
Cross-bred  races,  222,  229 
Crossing,  and  evolution,  223 

between  races,  221,  225,  226, 
227,  228,  229,  232,  233,  236 
Cuba,  99 
Cumberland,  113 
Cunier,  F.,  118 
Cunningham,  J.  D.,  72 
Curled  hair,  53,  126,  127 
Cushing,  Harvey,  88,  89 
Cuvier,  1 14 
Cyclopia,  4,  193 
Cytolysin,  144 

D 

Dachshund,  40,  126,  215 

Daltonism,  112 

Dampier,  65 

Danforth,  C.  H.,  92,  iii,  180 

Darien,  65 

Darwin,  C,  3,  54,  60,  99,  102,  129, 
148,    149,    168,    169,    170, 
193,  205,  220,  240,  241 
Erasmus,  168 

Daughters  of  Brigham  Young,  143 

Davenport,  C.  B.,  27,  28,  29,  30, 
35,  39,  41,  43,  52.  53,  58.  75, 
95,  122,  123,  125,  141,  153,  157, 
158,  162,  163,  194,  195,  196,  197, 
200,  222,  235,  236 

Deafness,  120 

Deaf-mutism,  inheritance  of,  106, 
107 

Dean,  Bashford,  68 

Death,  causes  of,  237 
rates,  237,  238,  243 

Decay  of  teeth,  124 

Decline  in  birth-rate,  244,  245 

Deer,  blastocyst  of,  177,  178 

Defectives,  marriage  of,  161 

Deformities,  origin  of,  71 

Dementia  praecox,  156,  158 

Democratic  Societ^^  221 

Denmark,  eye  colour  in,  45 


Departement  d'Isere,  104 
Descent  oj  Man,  102,  241 
Detlefson,  J.  A.,  69,  98,  iii 
Development  of  the  human  mind , 

225 
Dexter  Kerry  cattle,  216 
Diabetes  insipidus,  128,  236 
Differences  between  classes,  249 
Differential  birth-rate,  240,  249 
Differentiation  of  tribes,  226,  227 
Digital  abnormalities,  76 
Diploid  chromosome  numbers,  21 
Disharmonies,  physical,  222,  236 
Dislocation  of  the  lens  of  the  eye, 

130 
Disposition  in  twins,  180,  189 
Dizygotic  twins,  192,  202 
Dogs,  coat  colour  in,  67,  69 

eye  colour  in,  49 

length  of  tail  in,  68 

pariah,  41 

on  Sable  Island,  ij 

Polydactyly  in,  93 

prosopia  in,  126,  215 

turnspit,  41 

variations  in,  125 
Dolichocephalic  skulls,  212 
Dominance,  24 

variable,  55 
Dominant  factors,  174 
Donitz,  125 

Double  monsters,  179,  181,  199 
Double-yolked  eggs,  203 
Drawings  of  animals,  155 
Drinkwater,  H.,  80,  81,  82,  83,  85, 

86,  88,  90,  136,  170 
Drosophila,  17,  20,  25,  48,  90,  100, 

114,  132,  140,  196,  224 
Ductless  glands.     See   Endocrine 

glands 
Duerden,  J.  S.,  25 
Dugdale,  160 
Duke  Ernst  the  Iron,  124 
Duncan,  F.  N.,  89 
Duplicate    twins,    181,    182,    184, 

186, 188 
Dwarfness,  inheritance  of,  7 
Dwarfs,  human,  34,  35,  43,  44,  65, 
212,  215,  216 

trees,  36 

varieties,  36 
Dwight,  Timothy,  40 
Dynamometer  and  will  power,  i  55 


Ear,  bilobed,  135 

conformation  of,  25,  26 
lobe  fissure,  26 


INDEX 


277 


Ear,  lobe,  pitted,  135 
notch  in  cattle,  135 
pit,  inherited,  136 
Earl  of  Shrewsbury,  87 
Early  man,  cave  drawings  of,  155 
Ears  of  negroes,  236 

small,  in  house  mouse,  134 
East,  159,  ^45 
East  and  Jones,  20 
Edentates,  178 
Edentulism,  130 
Edwards  family,  160 
Eifect  of  body  on  mind,  166 
Effects  of  adrenalin,  218 
Elderton,  Ethel  M.,  146,  184 
Elimination  of  characters,  208, -209 

of  feeblemindedness,  169 
Ellis  Island,  232 
Embleton,  D.,  76,  ']'] 
Embryonic  budding,  176,  177,  178 

191'  199 

Emigration,  effect  of,  240 

Endocrine  glands,   153,   178,  210, 

211,  213,  217,  218,  228 

and  personality,  219,  220 

and     physiognomy,     64, 

142,  217 
and  temperament,  142 
Endoderm  and  death,  237 
England,  237 

deaf  mutes  in,  107 
population  of,  244 
and  Wales,  birth-rate  of,  239 
English  in  crosses,  228,  230,  231, 

232 
Enriques,  Paolo,  114 
Environment,   4,    5,   6,    145,    146, 
190,  227 
effect  on  character,  145 
on  wild  horses,  38 
Epidermolysis  bullosa,  127 
Epilepsy,  154,  155,  163,  164,  220, 

235 
and  feeblemindedness,  158 

Epiphyses  in  brachydactyly,  81 

Epitarsus,  116 

Eskimo,  stature  of,  28,  43 

Estabrook,  A.  H.,  149,  160 

Eugenic  action,  173 

matings,  160 
Eugenics,  aims  of,  204 
Eunuchoid  races,  2 1  5 
Evening  primroses,  206 
Evolution  and  crossing,  223,  233 

and  isolation,  224 

in  man,  225,  226,  246,  248 

of  civilization,  247 

of  mentality,  152 
Exogamy,  227 


Expression  in  twins,  187 

Eye  colour,  inheritance  of,  25,  27, 

44.   5S.   H5.   187.  207, 
229 
primitive,   64 
defects,  1 16,  130 
Eyelids,  constricted,  un) 
Eyes,  absence  of,  120 
of  negroes,  236 


Facial  types,  219,  224 
Fackenheim,  J.,  97 
Factors,  dominant,  174 

growth,  28,  7,1 

inhibiting,  35 

lethal,  90,  114,  140.  174,  i(j6, 
197,   209 

multiple,  27,  33,  34,  39 
Farabee,  W.  C,  78,  82 
Farmer,  J.  B.,  20 
Fasciation  of  stems,  5 
Fay,  Edward  A.,  107 
Fear  and  bodily  changes,  2 1 7 
Fecundity  of  man,  241,  243 
Feeblemindedness     and      Paheo- 
lithic  man,  225 

arrested  development  in,  235, 
247 

inheritance  of,  17,  147,  149, 
150,  154,  156,  157,  i:;S,  161, 
166 

in  pigeons,  167 

in  relation  to  insanity,  155 
Feebleminded   in    United    States, 
152,  158,  159,  160,  232 

reproduction  in,  251 
Femur,  length  in  deer  mouse,  i^^ 
Feral  animals,  36,  38 
Ferguson,  G.  O.,  234 
Fertilised  eggs  in  hybrids,  16 
Fildes,  Paul,  no,  114 
Filipinos,  hair  of,  53,  54 
Finger  prints,  175,  176,   180,   1S2, 

183 
types  of,  175,  184 
Fischer,  Eugen,  55,  56,  229 
Fisher,  R.  A.,  108 
Fishes,  cyclopean,  4 

eggs  of,  177 

hermaphroditic,  133 
Flexure  of  finger  joint,  193 
Flinders- Petrie,  221 
Flower-size,  inheritance  of,  ^3 
Folker,  H.  H.,  116 
Formula  for  growth  of  population, 

245 
Formulae  for  ancestral  influence, 

210 


2/8 


HEREDITY  AND  EUGENICS 


Formulge  for  systems  of  breeding, 
208 

Fowls,  brachydactyly  in,  92 
eye  colour  in,  50,  51 
hermaphroditism  in,  132 
Polydactyly  in,  93,  95,  97 

Foxes  on  Sable  Island,  n 
prognathism  in,  1 2  5 

France,  246 

Frederick  Wilhelm  of  Prussia,  43 

Free-martins,  198,  200,  202 

French  in  crosses,  231 

Frequency  of  twins,  194 

Freud,  165 

Friedenthal,  Hans,  54 

Frobelius,  1 30 

Frogs,  change  of  sex  in,  132 

■Functional  inheritance,  144 

Fusion  of  races,  223 


Gaits  in  twins,  190 

Gallic  tribes,  239 

Galton,    Sir  Francis,   2,   27,    149, 

175,  184,  187,  188,  193,  209 
Gamboge's  Raleigh,  135 
Garden  peas,  heredity  in,  8 
Gastropods,     reversed    symmetry 

in,  72 
Gastrula  of  armadillo,  177 
Genius  and  ability,  222 

and  insanity,  155,  156 
Georgia,  109 
Germans  in  crosses,  230 
German  tribes,  239 
Germany,  65,  137,  160,  246 

birth-rate  of,  239 
Germ  cells,  14 
Germinal  change,  5,  13 
Germ  plasm,    144,    156,   159,  209, 
210,  217,  250 

recessive  characters  in,  1 9 
Gigantism,  41,  42,  43,  loi,  212 
Gilpin,  J.B.,  36,  ^7^,  Z^ 
Glaucoma,  116 
Gluteal  prominences,  1 30 
Goats  and  goitre,  215 

breed  in  Kentucky,  166 

on  Sable  Island,  37 
Goddart,  149,  150,  152,  153,  155, 

232 
Goitre,  215 

Goldsmith,  W.  M.,  133 
Gorilla  and  pituitary,  217 
Goring,  Chas.,  139,  140 
Gossage,  A.  M.,  127 
Gowen,  John  W.,  202 
Gower's  disease,  sex-linked,  no 


I    Greece,  downfall  of,  238,  245 
Greek  race,  205 

in  crosses,  230 
Grey  hair,  inheritance  of,  25,  53 
Growth  curves,  32 

of  population,  245 

hormones,  41 
Guinea-pigs,    coat   colour  in,   48, 

125 
eye  colour  in,  50 
palsy  in,  167 
Polydactyly  in,  93,  94 
I  resistance  to  tuberculosis  in, 

140 
Guyer,  M.  F.,  20,  154 
Guyer  and  Smith,  144 
Gynandromorphs,  human,  131 

H 

Haddon,  A.  C,  223 
Haecker,  V.,  124,  125 
Haemophilia,  no,  114 
Haemorrhoids    in    negro    troops, 

235 
Hag-fisher,  albino,  68 

Hair,  absence  of,  55 

characters,    53,   54,    55,   214, 
217 

colour,  224 

inheritance  of,  25,  51,  53, 
145,  187,  190,  229 

distribution  of,  54 
Hairiness,  126 
Hairy  face,  55 
Hallam,  Colonel,  99 
Hamburghs,  gold-pencilled.  31 
Hancock,  Thomas,  n 
Handwriting,  108,  171,  172 

in  twins,  187,  189,  190 
Hanna,  G.  D.,  133 
Hapsburg  jaw,  88,  124 
Hardy,  164,  208 
Hare-lip.  130 
Harman,  N.,  59,  no,  in 
Harrison,  92 

Hawaii,  racial  crossing  in,  230 
Hawkes,  Onera  A.  M.,  106 
Hayden,  C.  C,  198 
Hay  fever,  inheritance  of,  138 
Health,  inheritance  of,  145 
Hemeralopia,  115 
Hennig,  103 
Heptadactyly,  102 
Herbivora,  multiple  births  in,  200 
Heyeditayy  Genius,  149 
Heredity,  2,  4,  6,  8,  237,  251 

defined,  7 

limits  of,  175 


INDEX 


279 


Hermaphroditism,   130,   132,   133, 

193,  201 
Hermaphroditismus     masculinus, 

193 
Heron,  151 

Heterochromidia  iridis,  49,  61 

Heterodactyly,  95 

Heterosis,  29,  205,  206,  230,  231, 

232 
Heterozygous,    characters    redis- 
tributed, 173 
defined,  10 
dominants,  16 
Hexadactyly,  75,  93,  95,  102,  103, 

104,  105,  193 
Hill  folk,  160 

Hindu  Amil  community,  71 
Hipparion-toes,  96 
Hoffman,  H.,  158 
Holden,  Jane,  122 
Holmes,  S.  J.,6i,  150,  152,  156,245 
Homer,  38 
Homozygous,  defined,  1 1 

condition  in  man,  192,  206 
Honduras  piebald,  59 
Hooper,  J.  J.,  166 
Hope  and  French,  126 
Hormones,  30,  33,41,42,201,210, 

215,  216,  217,  219,  220 
Home,  J.,  107 
Hornlessness,  126 
Horses,  albino,  71 

colouf  of  wild,  38 

dwarf,  35 

eye  colour  of,  49 

inheritance  in,  99 

intoxication  by  pampas  grass, 

167 
on  Sable  Island,  ^6,  ^y 
Polydactyly  in,  93,  96,  97 
Horstmann,  Elizabeth,  103 
Hottentots,  crosses  of,  229 
food  of,  227 
stature  of,  43 
women,  130 
Hover,  J.  M.,  142 
Howe,  Lucien,  94,  116 
Huddart,  Joseph,  113 
Huestis,  R.  R.,  33 
Humours  in  the  blood,  219 
Humphreys,  Col.  David,  40 
Hungarian  immigrants,  232 
Hunter,  John,  63,  201 
Huntingdon's  chorea,  156 
Hunting  rights  of  primitive  man, 

227 
Hurlin,  R.  G.,  99,  loi 
Hurst,   C.  C,  44,  49,   51,  71,   75, 
149,  167,  170 


Huxley,  93 
Huxley,  J.,  132 

Hybridization  in  man,  223,  238 
Hybrid  origin  of  races,  223 

races,  228,  229 

vigour,  205,  206,  230,  232 

walnuts,  205 
Hydrocele,  193 
Hyperdactyly,  10 1 
Hyperkinetic  temperaments,  162, 

164 
Hyperpituitary  face,  220 
Hypertrichosis,  130 
Hypodactyly,  105 
Hypophalangy,  90 
Hypophysis,  41 
Hypospadias,  130,  193 
Hypothyroidism,  215,  216 
Hypotrichosis,  128 
Hysteria,  163,  164,  235 


Ichthyosis,  117,  118,  122,  127 
Idiocy  in  Jews,  142,  158 
Idiots,  149,  153,  156,  157,  215 
Illinois,  97 

Illness  in  twins,  188,  189,  190 
Imbeciles,  149,  154,  155,  156,  157 
Immigrants  in  United  States,  27,2, 

236 
Inbreeding,    140,    143,   206,    207, 

208.  209,  223,  238 
India,  41,  71,  243 
Indians,  American,  stature  of,  28, 

30,43 
crosses  of,  231 
horses  of,  38,  223 
lefthandedness  in,  J2 
tribes  of,  223,  226,  227 
white,  65 
Industry  and  population,  241,  242 
Infanticide,  71,  238,  241,  243 
Inge,  Dean,  238,  244 
Inheritance,  2 

alternative,    7,    27,   99,    147, 

148,205,  223,  229,  232 
blended,  27,  52,   232 
functional,  144 
in  horses,  99 
in  twins,  176,  179,  i8u 
Mendelian,  9 
mental,   145,    149,    1O4,    1O5, 

166,'  168,  170,  186 
of  ability,  145,  147,  148,  149, 

250 
of    abnormalities,  9,   75,   76, 
106,  116,  125.  127,  129,  130 
of    absence   of  external   ear, 

133.  134 


2  8o 


HEREDITY  AND  EUGENICS 


Inheritance  of  absence  of  patella, 
136 
of  acquired  characters,  5 
of  artistic  ability,  1 70 
of  athletic  power,  145 
of  auricular  height,  145 
of  bilateral  asymmetry,  191 
of  bilobed  ear,  135 
of  bimanual  synergia,  136 
of  branchial  fistula,  1 30 
of  bronchial  asthma,  1 38 
of  calcar  loop,  1 76 
of  cancer,  140 
of  cephalic  index,  145 
of  character,  147 
of  cheek,  one  large,  i  ^(^ 
of  cleft  palate,  130 
of  clonic  spasms  in    guinea- 
pigs,  167 
of  coloboma,  116,  120,  130 
of  colour-blindness,  19,  22,  24, 

110,112,113 
of  constricted  eyelids,  109 
of  criminality,  163 
of  curliness  of  hair,  145 
of    differences    in   endocrine 

glands,  142 
of  disposition,  147 
of  dwarfing,  34 
of  edentulism,  1 30 
of  effect  of  cytoly sin,  144 
of  eye  colour,  145 
of  fingerprints,  175,  176,  180, 

182,  183,  184 
of  gait,  3,  190 

of  gluteal  prominences,  1 30 
of  hair  colour,  145 
of  handwriting,  108,  145 
of  hare-lip,  130 
of  hay  fever,  138 
of  hermaphroditism,  130,  131, 

132,  133 
of  hypertrichosis,  1 30 
of  hypospadias,  1 30 
of  insanity,  155,  156 
of    iso-agglutinin    reactions, 

129 
of  Jewish  physiognomy,  142 
of  luxation  of  femur,  1 30 
of  mathematical  ability,  147, 

149 
of  mental  differences,  145,146, 

147.236 
of  musical  ability,  147,  149 
of  mutilations,  26 
of  neurofibromatosis,  141 
of  notch  in  ear  of  cattle,  135 
of  openings  in  parietal  bones, 

U3 


Inheritance  of  peculiarities  of  the 
blood  system,  137 
of  personality,  220 
of  pitted  ear-lobe,  135 
of  polydactylism,  76,  92,  93, 
94,  96,   97,    loi,  .102,   103, 
126,  130,  180 
of  polymastia,  129 
of  rudimentary  ear-lobes,  133, 

134 
of  savageness  in  rats,  167 
of  scute  peculiarities  in  the 

armadillo,  181 
of  size,  26-35 
of  stammering,  141 
of  strabismus,  115,  120,  130 
of  temperament,  147,  236 
of  tendency  to  blush,  3 
of  timidity  in  rats,  167 
of  tuberculosis,  139 
of  tumours,  140 
of  twinning,  178,  194 
of  warts  on  the  hands,  123 
of  wildness  in  rats,  165,  166, 

167 
particulate,  27 
sex-linked,  19,  23,  25,  47,  61, 

no,  112,  114,  115,  116,  117, 

118,    120,    122,    123,    124, 

154,  163 

through  the  Y- chromosome, 
94,  loi,  1 19,  210 
Innocuous  characters,  207 
Insanity,  154,  155,  157,  166,  18S 
Instincts  in  man,  165 
Intelhgence,    157,    171,    190,   224, 

233.  234,  243,  246,  248,  249 
Intermarriage  of  strains,  222 
Intersexes,  131,. 132,  193,  201 
Interstitial  tissue  of  the  gonads, 

211,  212 
Intoxication  in  animals,  92,  167 
Introduced     animals     on     Sable 

Island,  ^y 
Iodine,  in  thyroxin,  214 

in  water,  215 
Iowa,  99 
Ireland,  49 

deaf-mutism  in,  106,  107 

over-population  in,  243 
Irish  in  crosses,  230 
Iso-agglutinin  reactions,  129 
Isolation  and  origin  of  differences, 

224,  226,  227,  238 
Italians,  in  crosses,  230,  233 

immigrants,  232 

stature  of,  30 
Italy,  pellagra  in,  122 

white  cattle  in,  71 


INDEX 


281 


Jamaica,  52 
Japanese,  Aino,  54 

and  modern  science,  226,  248 

dwarf  trees,  36 

in  crosses,  230,  231 

race,  2 1 5 
Jaw  appendages,  126 
Jenks,  A.  E.,  26,  135 
Jennings,  H.  S.,  208 
Jewish  race,  141 
Jews,  142,  158,  232 
Jones  and  Arnold,  167 

and  Mason,  1 1 1 
Jordan,  H.  E.,  53,  71,  yi 
Joseph,  Wilham,  10 1 
Jung,  165 

K 

Kaleia,  Gratio,  103 

KalHkaks,  160 

Kalmucks,  ears  of,  1 34 

Karakul  sheep,  135 

Kassowitz,  34 

Keith,  Sir  Arthur,  211,  212,  213, 

214,  215,  216,  217 
Kempf,  Edward  J.,  165,  168,  169 
Kempton,  J.  H.,  35 
Kentucky,  43,  166 
Keratosis,  5,  75,  121,  127 
Key,  Wilhelmine,  160,  162 
Kindred,  J.  E.,  136 
Klebs,  131 

Koch,  Mathilda  L.,  109 
Kiihn,  J.,  125 


Lactation     period     in     primitive 

races,  241 
Lambert,  Edward,  120 
Lane,  W.  C,  109 
Languages  of  Indian  tribes,  227 
Laplanders,  231 
Laughlin,  H.  H.,  209,  210 
Law  of  ancestral  inheritance,  209 

of  diminishing   returns,    241, 
242 

of  Malthus,  240 

of  Nasse,  1 10 
Lawrence,  T.  W.  P.,  131 
Learmonth,  J.  R.,  129 
Lebistes  reticulatus,  94 
Le  Compte  family,  1 17 
Left  -  handedness,    frequency    of, 
72 

inheritance  of,  71,  90 

measurement  of,  73 
Lemna  minor,  42 


Length  of  digits  in  foot,  106 

Lenz,  Fritz,  1 10 

Lepidoptera,  64 

Leporata,  Francesco,  43 

Lepra  bacillus,  123 

Leprosy,  123 

Lepus  variabilis,  69 

Lethal  factors,  90,  114,  140,   174, 

196,  197,  209,  217 
Leucoderma,  66 
Lewis,  T.,  76,  77,  78.  84,  93.  140 
LiUie,  F.  R.,  201 
Little,  C.  C,  67,  230 
Little  and  Gibbons,  114 
"  Lobster  claw,"  75,  76,  91 
Loeb,  Leo,  140,  141 
London,  55 

Lort,  Rev.  Michael,  112 
Louisiana,  63,  99 
Love,  A.  G.,  235 
Love,  J,  K.,  107 

Lundborg,  H.,  106,  108,  158,  231 
Lush,  J.  L.,  135 
Luxation  of  the  femur,  1 30 
Lynch,  Clara  J.,  134 


M 

MacBride,  E.  W.,  144,  178 
MacCaughey,  V.,  230 
MacDonald,  James,  70 
MacDougal,    Wilham,     146,     147, 

168,  248,  249,  250 
Machin,  John,  120 
Mackinder,  D.,  90 
McMullen,  Geo.,  78 
Magdalenian  man,  247 
Maine,  1 10 

Maize,  brachysm  in,  35 
Malays,  215,  248 
Malformations,  inheritance  of,  1 30 

in  twins,  192 
Maltese  family,  93,  103 
Malthus,  240,  241,  242 
Mameluco,  228 

Mammals,  variations  in,  125,  126 
Mandan  Indians,  hair  of,  53 
Mandibles  of  deer  mouse,  ^^ 
Manic  depressives,  158 
Manner  in  twins,  187 
Manson,  J.  S.,  10 1 
Manual  education  for  negro,  235 
for    mentally    defective, 
150 
Marchaud,  103 
Marriage  selection,  160 

control  of,  162,  244 
Martin,  P.  J.,  122 
Maryport,  1 1 3 


282 


HEREDITY  AND  EUGENICS 


Massachusetts,  36,  40,  65,  94 
Mathematical  ability,  inheritance 
of,  147,  149 
laws  of  inheritance,  207 
Measuring    scale    of    intelligence, 

149 
Medici,  de,  Catherine,  44 
Mediterranean  race,  2 1 2 
Meiosis,  defined,  15 
Melancholia,  158 
Melanism  in  Lepidoptera,  64 
Melanogenesis,  53 
Mendel,  8,  14,  17 

Mendelian,  dominant,  25,  60  75, 
76,  78,  88,  89,  90,  103,  105, 
109,  no.  III,  114,  117,  124, 
126,  127,  128,  133,  135,  136, 
141,  156,  208 
inheritance,  9,  14,  17,  24,  48, 

52,  T2,  207 
population,  208,  209 
recessive,  106,  107,  108,  109, 
no.  III,  115,  122,  134,  138, 
149,  150.  158,  167,  173.208, 
217 
Mental  capacity  of  modern  man, 
225 
characters,     inheritance     of, 
145,  164,  166,  168,  170,  186, 
188,  221 
complexes,  165 
defects,  154,  188 
evolution,  226 
instability  in  crosses,  231 
tests  for  immigrants,  232 
of  negroes,  234 
Mentality  of  man,  165 

of  negro,  234,  235,  247,  248 
Menzies,  Sir  W.,  98 
Mesenchyme,  hereditary  inferiority 

of,  142 
Metchnikoff,  131 
Mexico,  65 
Mice,  cancer  in,  140 
waltzing  ,167 
wildness  in,  167 
yellow,  196 
Microcephaly,  133 
Microphthalmus,  116,  120,  130 
Migraine,  163 
Migrations,  223,  226,  239 
Miller.  N.,  62 
Milroy.  W.  F..  127 
Minnesota,  69 

Minor  brachydactyly,  82,  88 
Minutiae  of  finger  prints,  175,  176, 

183 
Mirror-image    patterns.   176.   179, 
182 


Mirror- writers,  73 
Miscarriages,  196,  198 
Miscegenation,  222,  233,  236,  239 
Mivart,  St.  George,  125 
Mixture  of  races,  223,  236 
Mjoen.J.  A.,  231 
Mohr,  O.  L.,  89,  90,  91 
Momentary  blindness,  117 
"  Mongolian,"  152,  153 
Mongoloids,  features  of,  214,  215 

pituitary  of,  212,  214 

stature  of,  28 
MoniUthrix,  128 
Monkey,  chromosomes  of,  2 1 

Polydactyly  in,  93 
Monomaniac  twins,  188 
Monozygotic  twins,  191,  192,  199, 

202 
Montezuma,  65 
Montgomery,  20 
Montpelier,  114 
Moore,  20 

Mores  and  society,  163 
Morgan,  T.  H.,  196 
Morons,  149,  i5o,n^2,  154,  157 
Mott,  F.  W.,  158 
Mouse,  Californian  deer,  33 

house,  mutation  in,  1 34 
Mousterian  man,  225 
Mulattoes,  52,  53,  234 
Multiple  births  in  man,  197,  200 

factors,  27,  I},,  34,  39,  167 
Musical  ability,  inheritance  of,  147, 

149,  170,  171 
Mutations,  13,  17,  38,  41,  64,  66. 
68,  70,   75,  Tj,  85,  95,  99, 
109,  III,  125.  134,  140,  151. 
174,  175,  207,  217 

following  crossing,  59,  63 

parallel,  125 

sex-linked,  20 
Myoclonus-epilepsy.  108,  158 
Myopia,  115,  1 16 
Myxoedema,  214 

N 

Nam  family,  160 

Napoleon,  personality  of.  220 

Nasse,  law  of,  no 

Native  races,  207 

Natural  selection,    175.  207,  209, 

211,  240,  243,  246 
Naval  officers,  heredity  in,  164 
Neanderthal  skull,  216 
Negrillo  Akkas,  43 
Negroes,  brain  of,  233 

compared  with  whites,   235, 
236 


INDEX 


283 


Negroes,  crosses  of,  233 
features  of,  214 
hair  and  skin  of,  52,  54,  59,  6^ 
lefthandedness  in,  72 
mentality  of,    152,  234,  247, 

248 
pituitary  in,  212 
Polydactyly  in,  93,  loi 
Negro,  troops  in  American  army, 
225 
twins,  180 
Nelson,  164 
Neolithic  races,  223 
Nervous    derangements,     inherit- 
ance of,  166,  167 
system,  differences  inherited, 
210,  220 
of  negroes,  235 
Nettleship,  E.,   57,  61,    no,    114, 

116 
Neuralgia,  235 
Neurasthenia,  218,  220,  235 
Neurofibromatosis,  141 
Neurotic  stocks,  156 
Newman,   H.    H.,    115,    119,176, 

177,  178,  181,  199 
New  York,  foreign  born  in,  236 

sex-ratios  in,  230 
Nichols,  202 
Nietzsche,  220 
Night-blindness,  68,  75,  114,  115, 

116,  189 
Nilsson,  M.  P.,  238 
Nineveh,  sculptures  of,  ^y 
Nomadism,  162,  163 
Nordic  race,  141,  212,  231 
Norfolk  Islanders,  228 
North  Carolina,  43,  115 
Norway,  90,  134,  141,  104 
albinoes  in,  65 
deaf-mutes  in,  106 
eye  colour  in,  45,  48 
Polydactyly  in,  96 
racial  crossing  in,  231 
Nose-bleed,  hereditary,  109 
Notch  in  ear  of  cattle,  135,  203 
Nougaret,  Jean,  115 
Nucleus,  in  mitosis,  13 
Nyassaland,  59,  71 
Nyctalopia,  117 
Nystagmus,  1 16 

O 

Oats,  bush  varieties  of,  35 
Occipital  meningocele,  193 
Ocular  defects  in  twins,  190 
CEdema,  angioneurotic,  127 

persistent     hereditary,      126, 
127 


GLnothera  gi^as,  21 

Lamarckiana,  21 

bud  colours  in,  58 

chromosome  numbers  in,  21 

flower-size  in,  t^t^ 

self-pollination  in,  206 
Ohio,  158,  197,  198 
Openings  in  parietal  bones,  133 
Ophthalmia  in  twins,  188 
Optic  nerve,  atrophy  of,  116 
Optimum  density  of  population, 

242, 243 
Orang  and  thyroid,  2 1 7 
Ordahl,  G.,  157 
Organic  social  condition,  249 
Organism,    relation    to    environ- 
ment, 6 

development  of,  14 
Osborn,  Dorothy,  25 
Osteopsathyrosis,  75 
Ostrich  hybrids,  26 
Otis,  Arthur  S.,  157 
Otosclerosis,  107 
Ottawa,  39 

Over-population,  243,  244 
Oxford  class  lists,  146 


Pain  and  bodily  changes,  2 1 7 
Painter,  T.  S.,  21 
Palaeolithic  man,  151, 

mental    states    of,    225, 
226,  247,  248 
races,  223,  225 
Palm  and  sole  patterns,  176 
Palsy  in  guinea-pigs,  167 
Pancreas,  2 1 1 
Parathyroid  glands,  2 1  i 
Pariah  dogs,  41 

Parietal    bones,    conformation    of 
left,  193 
openings  in,  133 
Parthenogenctic  larvae,  178 
Parthenon,  38 
Patagonia,  38 

population  in,  242 
Patella,  absence  of,  1 36 
Patiria,  178 

Patterson,  J.T.,  176,  177,  181,  199 
Pearl,    Raymond,    92,    198,    208, 

229,  230,  237.  245 
Pearson,  Karl,  34,  35,  44,  52,  57, 

58,  59,  60,  61,  64,  65,  66,  68.  77, 

78,  139,  145,  146,  151,  153,  157. 

171,  208,  209 
Peas,  bush  varieties  of,  35 
Peculiarities  of  blood  system,  137 
Pekinese  dogs,  69 


2  84 


HEREDITY  AND  EUGENICS 


Pellagra,  122,  123 

Pelvic  bones,  length  in  deer  mouse, 

33 
Pennsylvania,  79,  160,  161 
Percy,  Harry  (Hotspur),  62 
Peromyscus  maniculatns,  ^,3 
Personality,  219,  221 
Pfitzner,  10 1 
Phaseolus  vulgaris,  206 
Phlegmatic  temperaments,  162 
Philippines,  180 
Phocomelia,  193 
Phrenology,  220 

Piebaldism,  2>^,  50,  59,  61,  66,  6y 
Pigeons,  ataxia  in,  109,  167 

eye  colour  in,  50,  51     . 

Polydactyly  in,  95 

twins  in,  203 

sex-ratio  in  crosses,  230 
Pigs,  abnormal  race  of,  99 

corpora lutea in, 196 

on  Sable  Island,  36,  T)J 

Polydactyly  in,  97 

syndactyly  in,  98 
Pima  Indians,  72 
Pineal  gland,  142,  211 
Pinus,  polyembryony  in,  179 
Pitcairn  Island,  228 
Pit  in  skin,  inheritance  of,  1 36 
Pitted    ear-lobes,   inheritance  of, 

135 
Pittsburg  school-children,  249 

Pituitary  and  personality,  219 

and  size,  32,  35,  41,  43,  142, 
211,  212 

in  gorilla,  217 
Pituitocentric  personalities,  220 
Pityriasis  versicolor,  123 
Plane-tree  in  London,  205 
Plate,  106 
Pliny,  10 1 

Pneumonia  in  negro  troops,  235 
Poa  argent ina,  167 
Pollen  grains  of  rice,  1 5 
Polydactjdy,  76,  92,  93,  94,  96,  97, 

loi,  102,  103,  126,  130,  180 
Polyembryony,  in  armadillo,  176, 
177,178 

in  pines,  179 
Polymastia,  102,  129 
Polynesians,  43,  228 
Polyuria,  128 
Pond,  Clara  P.,  10 1 
Ponies,  Chinese,  35,  126 

Sable  Island,  36 

Shetland,  35,  36 
Pontianak,  Sultan  of,  103 
Poole,  65 
Popenoe,  Paul,  143,  164,  190 


Population,    239,    240,    241,    244', 

245,  246 
"  Porcupine  man,"  120 
Porokeratosis,  128 
Portuguese  in  crosses,  228,  23U 
Poultry,  Polydactyly  in,  95 

weight  in,  31 
Prepotency,  142,  143 
Pribiloff  Islands,  133 
Priestley,  Rev.  Joseph,  1 1 3 
Primitive  culture,  225 

man,  226,  227,  241,  243,  248 
Primula,  self  sterility  in,  224 
Prognathism,  124,  125 
Protozoa,  41 

behaviour  in,  165 
Prussia,  199 

Psychical  characteristics,  146 
Psychoanalysis,  166,  168,  170 
Psychological     analysis     of     the 

mind,  147,  164 
Psychology,  165,  168 
Psychopathology,  165,  168 
Pterygium,    116 
Ptosis,  116 

Puberty  and  stature,  4 1 
Punnett,  R.  C,  9,  31,   159 
Pure  lines,  221 
Pygopagous  twins,  179 


Q 

Quadruplets    in    armadillo,     176, 
181,  182 
in  man,  197,  200 
Quantitative  characters,  9,  213 
Quantity  in  population,  245 
Queen  Charlotte  Islands,  Indians 
of,  65 

R 

Rabbits,  colour  in,  48,  125 
corpora  lutea  of,  1 96 
eye  colour  in,  49 
inheritance  of  size  in,  29,  32 

weight  in,  31 
injection  of  serum,  144 
on  Sable  Island,  ^7 
Racial  characters,  9 

in  man,   210,   211,   214,   217, 

224 
crosses,  213,    221,    224,    228, 
229,230,231,232,233,236 
Radiographs,  80,  85 
Rage  and  bodily  changes,  217 
Raleigh,  164 
Ramaley,  F.,  72 
i    Random  mating,  208,  209 


INDEX 


285 


Rats,  cancer  in,  140 

inheritance    of    wildness    in, 
165,  166 
of  waltzing  in,  167 

on  Sable  Island,  i"] 
Ray  pattern  eye  colour,  49 
Reaumur,  93,  103 
Reduction  divisions,  14,  15,  20,  24 
Reed,  L.  J.,  245 
Reheboth  hybrid  people,  229 
Reproductive  overwork,  109 
Reptiles,  hermaphrodites  in,  133 
Resemblances,  inheritance  of,  24 

in  identical  twins,  200 
Retinitis  pigmentosa,  116 
Reversed  symmetry,  72,  179 
Rice  hybrids,  i  5 
Rickets,  42 
Riddle,  O..  109,  167 
Ridge  patterns  of  finger  tips,  176, 
180, 183 
of  palms  and  soles,  176, 
179 
Rieder,  H.,  91 
Rischbieth,  H.,  34,  130 
Ritzman,  E.  G.,  134 
Roberts,  Elmer,  97,  98 
Robins,  albino,  68 
Rodentia,  multiple  births  in,  200 
Roman  rule,  238,  239 
Rome,  downfall  of,  238,  245 
Rontgen  rays,  141 
Rudimentary  ear  lobules,  1 34 
Riidin,  Ernst,  i  58 
Russians,  immigrants,  232 

in  crosses,  230 


Sable  Island,  36,  38 

wild  horses  on,  37 
Salaman,  R.  N.,  141,  142 
Salamanders,  41,  42 
Saltations,  126 
Samar  Island  twins,  180 
San  Francisco,  39 
Sano,  F.,  186 
Santa  Cruz  Island,  39 
Sarcoma,  140 

Savageness,  inheritance  of,  167 
Scandinavians,  eye  colour  in,  64, 
207 
migrations  of,  239 
Schaefer,  218 
Schmidt,  Johs,  94 
Schofield,  R.,  61,  94,  100,  135 
Schroeder,  105 
Schultz,  A.  H.,  100 
Schurmeier,  100 


Schuster,  E.,  146 
Schwcizcr,  Marie,  103 
Scotch  in  crosses,  230 
stature  of,  30,  43 
Scotland,  albinism  in,  66 
deaf-mutism  in,  107 
Scott,  J.,  112 
Scurvy,  42 

Scutes  in  armadillo,  181 
Seals,  hermaphroditism  in,  133 
Sebaceous  scalp  tumours,  123,  124 
Sedgwick,  William,  25,  49,  53,  66, 
67,  76,  105,  117,  119,  120,  121, 
122,  123,  124,  133,  134,  136,  T55 
Sedigiti,  loi 

Seedlings,  right-handed,  74 
Segmentary  social  condition,  248 
Segregation  of  characters,   8,    13, 

15,  213,  222,  229 
Selection,  221,  223 

against  feeblemindedness,  159 
Self-fertilisation,  208,  209 
Self-pollination  in  CEnothera,  206 
Self-sterility  in  plants,  224 
Seligman,  C.  G.,  102,  216 
Sella  turcica,  41 
Serums,  26,  129,  144 
Sessions,  Mina  A.,  158 
Sex  chromosomes,  19,  132 
in  insects,  22 
in  man,  20,  22,  210 
Sex-determination,  19,  22,  201 
Sex-linked  inheritance,  19,  20,  47, 
61,  no,  112,  114,  115,  116,  117, 
118,    120,    122,    123.    124,    154, 
163 
Sex  of  twins,  195 
Sex-ratio,  in  crosses,  229,  230 
after  war,  239 
of  twins,  202 
Sexual  selection,  -jj ,  207 
Shattock,  S.  G.,  132 
Sheep,  Ancon,  40 
earless,  134 
horns  in,  61 
intoxicated  by  pampas  grass, 

167 
on  Sable  Island,  'S^ 
thyroid,  214 
twins,  194,  202 
Shelley's  face,  219 
Shell-shock,  218 
Shetland  ponies,  35 
Shifting  of  peoples,  223,  226,  239 
Siaynanga  syndaciyla,  100 
Siamese,  2 1  q 
Siemens,  H."W.,  158 
Simpson,  Q.  I.,  63 
Sinclair,  James,  70 


2  86 


HEREDITY  AND  EUGENICS 


Sinistro-dextral  ratio,  ^^ 

Size  factors,  29,  31 

Size  inheritance,  29,  30,  32,  34,  39 

in  plants,  S3 
Skiagraphs,  87,  10 1 
Skin  colour,  2,  4,  213,  224 

and  hormones,  212,  213, 

217 
inheritance  of,  51,  52,  58, 

64,  228,  229 
of  primitive  man,  6^ 
diseases  in  negroes,  235 
secretions,  224 
Slye,  Maude,  140 
Social  dominance  of  white  man, 

215 
ladder,  250 

organization    of    early    man, 

226 

Soudan,  43 

Spanish  in  crosses,  230 

Sparrows,  albino,  68 

Species,  interfertility  of,  224 

Spermatogenesis,  human,  20,  21, 

22,  158 
Spleen,  enlarged,  128 
Split  hand  and  foot,  y6,  78 
Sports,  175 

Spotting  of  skin,  58,  59,  63,  66,  67, 
68,69 
inheritance  of,  69 
Spread  of  culture,  227 
Squinting.     See  Strabismus 
Squirrels,  albino,  68 
Stability   of   savage   populations, 

227 
Stammering,  inheritance  of,  141 
Standard  of  living.  242,  243 
Standley,  Paul  C,  69 
Stannus,  H.  S.,  58,  59,  71 
Stanton,  H.  M.,  171 
Starfish,  twin  embryos  in,  178 
Stark,  140 

State  Eugenics  Board,  162 
Stature,  224 

and  hormones,  212,  217 
inheritance  of,  25,  27,  40,  41, 

43 
of  brachydactyls,  82 

of  twins,  187,  189,  190 
Sterility  in  free-martin,  201 

in  mankind,  196 

interspecific,  224 
Sternalis  muscle,  193 
Stieve,  H.,  92 
Still-births,  230 
St.  John,  Harold,  36 
Stockard.  C.  R.,  4,  176,  177 
Stone  Age,  225 


Storer,  Rev.  John,  70 
Strabismus,  115,  120,  130 
Stratification  of  society,  221 
Striping  of  flowers,  50,  58 
Stuckey,  H.  P.,  109 
Stuttering,  74 
St.  Vitus'  Dance,  156 
Subpituitary  face,  220 
Suetonius,  97 
Sulcus  intertragicus,  26 
Sullivan,  L.  R.,  180 
Sumner,  F.  B.,  6,  33 
Supernumerary,  breasts,  102,  129 

phalanx  on  thumbs,  92 
Sweden,  deaf-mutes  in,  106 

myoclonus  epilepsy  in,    108, 
158 

racial  crossing  in,  231 
Swedes,  stature  of  ,30 
Swingle,  W.  W.,  1 32 
Symmetry    in     armadillo     quad- 
ruplets, 181 
Syndactyly,  76  ,92,  93,  94,  98,99, 

100,  loi,  126 
Syphilis,  153 


Tahiti,  228 
Taillessness,  126 
Tallness,  inheritance  of,  7 
Tamias,  albino,  68 
Tansley,  A.  G.,  165 
Tarpany  horse,  ^y 
Tastes  in  twins,  189 
Tatusia  novemcincta,  i  jj 
Taurae,  201 

Teeth,  early  decay  of,  124 
Telangiectasis,     multiple     heredi- 
tary, 127 
Temperamental    differences,    142, 

143,  210,  248 
Temperaments,  142,  162,  219,  236, 

in  animals,  165 
Tendency     to     perform     certain 

tricks,  148 
Tetraploid  chromosome  numbers, 

21 
Tetraploidy,  42 

Texas,  21,  99,  115,  135,  176,  177 
Thadani,  K.  T.,  71 
Thalassophilia,  164 
Thessaly,  71 
Thorndike,  198 

Thumb  joint,  peculiarity  in  twins, 
190 

missing,  95 
Thyroid,  142 

and  baldness,  25 

and  race,  211,  212,  213,  215 


INDEX 


287 


Thyroid,  action  of,  215,  216,  217 

and  personality,  219 

and  size,  32 

cancer  in,  of  rats,  140 

composition  of,  214 
Thyroxin,  214,  216 
Timidity,  inheritance  of,  167 
Tissue  cultures,  41 
Titles,  hereditary,  222 
Tomatoes,  bush  varieties,  35 
Toothache  in  twins,  188 
Tooth  anomalies,  55,  97,  102,  124, 

130,  222,  236 
Toothless  families,  71 
Tortoiseshell-coloured  eyes,  49 
Tradition,  205,  225,  226,  247,  248, 

249 
Transforrhation  of  sex,  131,  132 
Tremor,  hereditary,  108 
Tribal  differences,  loss  of,  223 
Triplets,  197,  198,  199 
Triploid     chromosome     numbers, 

21 
Trivial  characters,  207 
Troph  oedema,  127 
Tuberculosis,  123,  139 

in  crossed  races,  231 

in  negroes,  235 
Tumbling  in  pigeons,  167 
Tumours  from  nerves,  141 

in  Drosophila,  140 

in  pituitary,  212 

sebaceous,  123 
Tupper,  W,  W.,  42 
Tiirdus  migratorius,  68 
Turkeys,  wild,  39 
Turnspit  dog,  41 
Twin  embryos,  production  of,  177, 

178 
Twinning,  influence  of  father  on, 

195 
inheritance  of,  194 
Twins,  76,  146,  173,  175,  176,  178, 
179,  180,  182-193 
effect  of  separation,  1 90 
in  cattle,  198,  201,  202,  203 
■    in  fishes,  177 
origin  of  identical,  199 
two  types,  1 98 

U 

Uhlenhuth,  E.,  41 

Unconscious  repression,  165 

Unilateral  inheritance,  135,  136 

Uniovular  twins,  180 

United  States,  237,  250 

Anglo-Saxons  in,  245 
arable  land  in,  245 


United' States,  births  in,  200 

crossingin,  230,  232,233, 

236 
feeblemindedness  in,  152, 

159 
negro  in,  233,  234 
pellagra  in,  122 
population  of,  245 

Urquhart,  A.  R.,  156 

Usher,  C.  H.,  44,  57,  61 

Uxbridge,  91 

■     V 

Variation,  i ,  5,6,  7 

blastogenic,  181 

continuity  in,   27,    i:;!,    17^, 
184 

discontinuity  in,  27,  175 

in  Canidae,  125 

in  hybrid  race,  229 

in  mammals,  125 

in  man,  21 1 
Vegetables,  bush  varieties  of,  35 

run  wild,  39 
Venereal  disease  in  negro  troops, 

235 
Vermont,  104 

Vigour  from  crossing,  29,  206,  223 

in  twins,  188 

Vineland  Institution,  1 50 

Virginia,  89 

Vitamines,  42 

Voice  in  twins,  187,  189,  190 

W 

Walker,  20,  84,  88 
Wallace,  A.  R.,  100,  228,  240 
Walnut  hybrids,  205 
Waltzing  in  mice,  167 
Warren,  H.  C,  207 
Warts  on  the  hands,  123 

inheritance  of,  123 
Washington,  Booker  T.,  235 
Weakening    of    a    character    by 

exogamy,  104 
Webbing. "   See  Syndactyly 
Weeks,  158 
Wegelin,  Carl,  91 
Weidenreich,  100 
Weight  in  twins,  187,  189 
Weinberg,  107,  108 
Weismann,  144 
West  Indies,  94 
Wheat,  bush  varieties  of,  35 

chromosomes  of,  22 

pure  lines  in,  221 
Whisson,  Rev.  Mr.,  112 
Whitchurch,  Sy 


288 


HEREDITY  AND  EUGENICS 


White  cattle,  70,  71 

forelock,  59,  60,  62 
Wieman,  H.  L.,  20 
Wilder,  H.  H.,  176,  179,  183 
Wildness,  inheritance  of,  165,  166, 

167 
Wild  horses,  37,  38 

turkeys,  39 
Wile,  10 1 
Windle,   C.   A.,   26,   43,   93,    129, 

137,  192,  193 
Wmge,  O.,  45,  46 
Winiwarter,  von,  20,  21,  22 
Witschi,  Emil,  132 
Wolff.  10 1 

Wolves,  cancer  in,  140 
Woodchucks,  albino,  68 
Worcester,  40 


Wriedt,  Chr.,  71,  89,  90,  134 
Wyat,  102 


Yapp,  W.  W.,  Ill 
Y-chromosome,    19,    23,    94,    10 1, 

1 19,  210 
Yearsley,  M.,  107 
Yellow  and  brown  races,  225 
Yerkes,  R.  M.,  166,  167 
Youatt,  99 
Young,  Brigham,  143 


Zeleny,  C,  199 
Zobnomia,  168 
Zygodactyly,  100 


ftonnTY  LIBURY 

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